Is this a hawk, or an eagle?

Is this a hawk, or an eagle?

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I saw this large bird gliding fairly low over the trees while hiking in the late afternoon in some hills near Taipei recently. It seemed quite large compared to what I normally see here. It's quite difficult to gauge, but I'd guess the wing span was one meter or so.

It made that shrill, descending, single "peeeew" sound that I associate with birds of prey (probably mostly from old movies or TV commercials).

Is it at all possible to guess if this is a hawk or an eagle from these cell phone snapshots? These are cropped out of the full resolution originals. A half-size original for scale is also included.

The words "hawk" and "eagle" are very confusing and may mean different things in different parts of the world. In fact, the nearly thirty species of raptors (not including owls) native to Taipei apparently include one called a mountain hawk-eagle (Nisaetus nipalensis).

If no one can answer your question, you might narrow the field with a process of elimination. I can't vouch for the accuracy of Wikipedia's list of birds native to Taipei, but it's a start.

There are apparently seven native raptors that are called eagles. If you can eliminate all seven eagles, then it presumably is not an eagle.

Your photographs are helpful insofar as they illustrate the bird's general outline, but it's very hard to distinguish its color pattern. However, the shape of the wings should help narrow the field.

Birds Native to Taiwan


I don't know if you're familiar with the terminology, but many raptors are classified as buteos or accipiters. If I remember correctly, species with broader wings are generally buteos. Species commonly called "hawks" include both buteos and accipiters, but I believe most birds called "eagles" are buteos.

Anyway, here's another link…


Bald Eagle Identification

Very large raptor with long, broad wings. Dark brown body contrasts with its white head and tail.


Juveniles have a brown body with brown and white mottled wings. The tail is also mottled with a dark band at the tip.


Voice is a high, weak-sounding whinny.


Amount of white in the wings is variable on juveniles.


When perched appears very large, with brown body and contrasting white head and bright yellow bill.


Often scavenges food or eats carrion.


Will hunt for fish when near water.

Fourth year

Fourth year birds look like adults with some brown feathers on the otherwise white head.

Adult with nestlings

Builds huge stick nests in trees, usually some distance below the top of the tree. Juveniles are mottled brown and white, with dark heads.

Second year

Second year birds are strongly mottled brown and white.

Second year

The amount of white feathering can be highly variable on juveniles and second year birds.


In flight, notice very long, broad wings held fairly flat. Large head just out ahead of the wings as far or farther than tail trails behind.

Third year

Third year birds have a mostly white belly, with some brown mottling, a brown chest, and a broad brown mask on the face.

Adult and juvenile

Will form groups during the nonbreeding season, when different age classes can be seen together.


Constructs enormous stick nests, usually in large trees.

What's a hawk chick doing alive in an eagle nursery?

Update (June 27, 2017): The red-tailed hawk – who's since been nicknamed "Spunky" – is still quite at home with its adopted eagle family, and according to reports from locals observing the nest, the young bird has now fledged! The hawklet took its first short flight late last week, and was able to make it back to the nest where it was fed by its bald eagle "parents". Read the full story behind this amazing avian "adoption" below – and check back in for updates! Here's a recent video of feeding time at the nest, taken just before Spunky fledged:

Exposure to the elements, sudden raids by predators, incompetent (or outright callous) parents, the omnipresent spectre of starvation: any baby bird faces some steep odds in its journey to full-feathered, high-flying adulthood. But one weeks-old red-tailed hawk in British Columbia has managed to beat odds that are both steeper and stranger than usual. How long it can keep doing so, though, remains a very open question.

This spring, bird watchers monitoring a long-used bald eagle nest along the seacoast of Vancouver Island's Saanich Peninsula noticed a strange-looking tenant amid three eaglets: a much smaller nestling identified as a newborn red-tailed hawk. The eagle parents have been feeding the hawklet alongside their own chicks, treating the imposter as a member of the family.

It's an unusual and fraught situation. Eagles and hawks aren't naturally chummy: brooding redtails (and other hawks) defensively harass much larger but less agile bald eagles, which in turn will readily prey on hawk nestlings.

So what's a hawk chick doing alive and (apparently) well in an eagle nursery? We can't say for sure, but local raptor experts suspect the likeliest scenario involves the eagles plundering a redtail nest and hauling some chicks back to their aerie as prey. Perhaps the hawklet in question, still kicking, started gaping for food and triggered the eagles' parental instincts.

Supporting this hunch is the fact that a local nature photographer actually took a picture on May 29 of two hawklets in the eagle nest. That second redtail chick didn't make it – eaten, perhaps, or simply a victim of the harsh, sometimes fratricidal competition common within eagle broods.

The surviving hawklet, though, has proved its mettle so far, successfully vying with its much heftier nest-mates for scraps. "It's quite something to see the way it is treated," Kerry Finley, a caretaker at the Shoal Harbour Migratory Bird Sanctuary where the eagle nest is situated, told the Vancouver Sun. "The parents are quite attentive."

Dr David Bird, retired professor of wildlife biology at McGill University and director of the Hancock Wildlife Foundation that's long kept tabs on this particular aerie, notes that the redtail likely assumes it's an eagle. "That's probably why it's so cocky and has a lot of swagger," he explains. "Because of its spunkiness and aggressiveness, it's been able to survive among those big eaglets."

The hawklet is obviously ascribing to an eagle's diet. "Let me put it this way: it's eating a lot of fish," Bird says. The eagle aerie – occupied for more than a quarter-century – lies in a Douglas-fir tree on Roberts Bay, with easy access to rich fishing and foraging waters in and along Haro Strait. The chick's mostly piscivorous menu isn't exactly typical for its kind, but Bird doesn't expect any long-term issues: red-tailed hawks, after all, are generalist predators up for eating just about anything they can catch and overpower.

Then again, "long term" isn't necessarily in the cards for a hawk in a bald-eagle foster family.

The eaglets hatched at the start of April, and observers estimate the hawklet to be roughly half their age – maybe five weeks old. It would, of course, be outsized regardless of any age disparity. A mature bald eagle may tip the scales at ten pounds or more and sports a wingspan of six or seven feet an average red-tailed hawk weighs four or five times less. You can see just how much smaller the hawklet is than its nestmates in this recent video of feeding time in the mixed brood:

Impressive as the youngster's ongoing survival literally in the heart of an eagle's nest has been, a perilous period lies ahead. Within the next couple of weeks, the hawklet and its adopted siblings will fledge. They'll leave the nest for longer and longer periods, practicing flight and eventually hunting. Mom and dad will still feed them for perhaps seven to ten days further, Bird explains, but it's something of a free-for-all: the adult eagles may just drop food in the nest, and the fledglings will have to scramble for it. At this stage, eaglets will even aggressively commandeer morsels from incoming parents.

It'll be a real test for the young hawk to muscle its way into this fray – and, as it does so, to avoid looking like dinner to the increasingly big, mobile and mature eaglets. Bird notes that it's also possible the eagle pair will wind down their parental duties before the redtail's adept enough to catch prey on its own.

Should the hawklet survive the trial-by-fire of its upbringing and successfully reach adulthood, Bird is especially intrigued by what sort of path it might take. "The redtail may or may not leave the nest safely," he says, "but if it does, will it try to court a bald eagle or court its own kind?" In other words, will it keep on assuming it's an eagle? (Just keep it away from a mirror.)

Decades ago, Bird and his colleagues conducted experiments into "cross-fostering" among raptors, specifically the little falcons called kestrels. The researchers swapped eggs and babies between American and common (aka European) kestrels, and then tracked their mating preferences as adults: would they shun their own species and romance potential partners belonging to their adopted one? "About 50 percent of them made the wrong choice," Bird notes.

Of course, should this foster-raised redtail try getting fresh with a bald eagle, it's unlikely to get very far. "It will probably be immediately rebuffed, if not killed," Bird says.

Even without self-identity issues and potentially murderous family members, a young raptor has its work cut out for it: about half die within the first year. Those are the cold hard facts, but we probably shouldn't be writing off this spunky red-tailed hawk just yet: it's got the outlook of an eagle, after all.

For the latest updates on the mixed-brood aerie, visit the Hancock Wildlife Foundation website, which maintains a wide variety of live-streaming nest cams (though not for this one).

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Originally Published July 5, 2017

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The red-tailed hawk was formally described in 1788 by German naturalist Johann Friedrich Gmelin under the binomial name Falco jamaicensis. [11] Gmelin based his description on the "cream-coloured buzzard" described in 1781 by John Latham in his A General Synopsis of Birds. [12] The type locality is Jamaica. [13] The red-tailed hawk is now placed in the genus Buteo that was erected by French naturalist Bernard Germain de Lacépède in 1799. [14] [15]

The red-tailed hawk is a member of the subfamily Buteoninae, which includes about 55 currently recognized species. [2] [16] Unlike many lineages of accipitrids, which seemed to have radiated out of Africa or south Asia, the Buteoninae clearly originated in the Americas based on fossil records and current species distributions (more than 75% of the extant hawks from this lineage are found in the Americas). [2] [17] As a subfamily, the Buteoninae seem to be rather old based on genetic materials, with monophyletic genera bearing several million years of individual evolution. Diverse in plumage appearance, habitat, prey, and nesting preferences, buteonine hawks are nonetheless typically medium- to large-sized hawks with ample wings (while some fossil forms are very large, larger than any eagle alive today). [18] [19] [20] The red-tailed hawk is a member of the genus Buteo, a group of medium-sized raptors with robust bodies and broad wings. Members of this genus are known as "buzzards" in Eurasia, but "hawks" in North America. [21] Under current classification, the genus includes about 29 species, the second-most diverse of all extant accipitrid genera behind only Accipiter. [15] The buzzards of Eurasia and Africa are mostly part of the genus Buteo, although two other small genera within the subfamily Buteoninae occur in Africa. [2] [16] [22]

At one time, the rufous-tailed hawk (B. ventralis), distributed in Patagonia and some other areas of southern South America, was considered part of the red-tailed hawk species. With a massive distributional gap consisting of most of South America, the rufous-tailed hawk is considered a separate species now, but the two hawks still compromise a "species pair" or superspecies, as they are clearly closely related. The rufous-tailed hawk, while comparatively little studied, is very similar to the red-tailed hawk, being about the same size and possessing the same wing structure, and having more or less parallel nesting and hunting habits. Physically, however, rufous-tailed hawk adults do not attain a bright brick-red tail as do red-tailed hawks, instead retaining a dark brownish-cinnamon tail with many blackish crossbars similar to juvenile red-tailed hawks. [2] [23] [24] Another, more well-known, close relative to the red-tailed hawk is the common buzzard (B. buteo), which has been considered as its Eurasian "broad ecological counterpart" and may also be within a species complex with red-tailed hawks. The common buzzard, in turn, is also part of a species complex with other Old World buzzards, namely the mountain buzzard (B. oreophilus), the forest buzzard (B. trizonatus ), and the Madagascar buzzard (B. brachypterus). [2] [22] [25] All six species, although varying notably in size and plumage characteristics, in the alleged species complex that contains the red-tailed hawk share with it the feature of the blackish patagium marking, which is missing in most other Buteo spp. [2] [26]

Subspecies Edit

At least 14 recognized subspecies of B. jamaicensis are described, which vary in range and in coloration. Not all authors accept every subspecies, though, particularly some of the insular races of the tropics (which differ only slightly in some cases from the nearest mainland forms) and particularly Krider's hawk, by far the most controversial red-tailed hawk race, as few authors agree on its suitability as a full-fledged subspecies. [5] [9] [27]

    (B. j. jamaicensis), the nominate subspecies, occurs in the northern West Indies, including Jamaica, Hispaniola, Puerto Rico and the Lesser Antilles, but not the Bahamas or Cuba. (B. j. alascensis) breeds (probably resident) from southeastern coastal Alaska to Haida Gwaii and Vancouver Island in British Columbia. (B. j. borealis) breeds from southeast Canada and Maine south through Texas and east to northern Florida. (B. j. calurus) seems to have the greatest longitudinal breeding distribution of any race of red-tailed hawk. (B. j. costaricensis) is resident from Nicaragua to Panama. (B. j. fuertesi) breeds from northern Chihuahua to South Texas. (B. j. fumosus) is endemic to Islas Marías, Mexico. (B. j. hadropus) is native to the Mexican Highlands. (B. j. harlani) breeds from central Alaska to northwestern Canada, with the largest number of birds breeding in the Yukon or western Alaska, reaching their southern limit in north-central British Columbia. (B. j. kemsiesi) is a dark subspecies resident from Chiapas, Mexico, to Nicaragua. (B. j. kriderii) breeds from southern Alberta, southern Saskatchewan, southern Manitoba, and extreme western Ontario south to south-central Montana, Wyoming, western Nebraska, and western Minnesota. (B. j. socorroensis) is endemic to Socorro Island, Mexico. (B. j. solitudinis) is native to the Bahamas and Cuba. (B. j. umbrinus) occurs year-round in peninsular Florida north to as far Tampa Bay and the Kissimmee Prairie south throughout the rest of peninsular Florida south to the Florida Keys.

Red-tailed hawk plumage can be variable, depending on the subspecies and the region. These color variations are morphs, and are not related to molting. The western North American population, B. j. calurus, is the most variable subspecies and has three main color morphs: light, dark, and intermediate or rufous. The dark and intermediate morphs constitute 10–20% of the population in the Western United States, but seem to constitute only 1–2% of B. j. calurus in western Canada. [28] [29] A whitish underbelly with a dark brown band across the belly, formed by horizontal streaks in feather patterning, is present in most color variations. This feature is variable in eastern hawks and generally absent in some light subspecies (i.e. B. j. fuertesi). [2] Most adult red-tails have a dark-brown nape and upper head, which gives them a somewhat hooded appearance, while the throat can variably present a lighter brown "necklace". Especially in younger birds, the underside may be otherwise covered with dark-brown spotting, and some adults may too manifest this stippling. The back is usually a slightly darker brown than elsewhere with paler scapular feathers, ranging from tawny to white, forming a variable imperfect "V" on the back. The tail of most adults, which gives this species its name, is rufous brick-red above with a variably sized, black subterminal band and generally appears light buff-orange from below. In comparison, the typical pale immatures (i.e. less than two years old) typically have a mildly paler headed and tend to show a darker back than adults with more apparent pale wing-feather edges above (for descriptions of dark morph juveniles from B. j. calurus, which is also generally apt for description of rare dark morphs of other races, see under that subspecies description). In immature red-tailed hawks of all morphs, the tail is a light brown above with numerous small dark brown bars of roughly equal width, but these tend to be much broader on dark morph birds. Even in young red-tails, the tail may be a somewhat rufous tinge of brown. [2] [4] [30] The bill is relatively short and dark, in the hooked shape characteristic of raptors, and the head can sometimes appear small in size against the thick body frame. [2] The cere, the legs, and the feet of the red-tailed hawk are all yellow, as is the color of bare parts in many accipitrids of different lineages. [31] Immature birds can be readily identified at close range by their yellowish irises. As the bird attains full maturity over the course of 3–4 years, the iris slowly darkens into a reddish-brown, which is the adult eye-color in all races. [4] [30] Seen in flight, adults usually have dark brown along the lower edge of the wings, against a mostly pale wing, which bares light brownish barring. Individually, the underwing coverts can range from all dark to off-whitish (most often more heavily streaked with brown) which contrasts with a distinctive black patagium marking. The wing coloring of adults and immatures is similar but for typical pale morph immatures having somewhat heavier brownish markings. [2] [27]

Though the markings and color vary across the subspecies, the basic appearance of the red-tailed hawk is relatively consistent.

Overall, this species is blocky and broad in shape, often appearing (and being) heavier than other Buteos of similar length. They are the heaviest Buteos on average in eastern North America, albeit scarcely ahead of the larger winged rough-legged buzzard (Buteo lagopus), and second only in size in the west to the ferruginous hawk (Buteo regalis). Red-tailed hawks may be anywhere from the fifth to the ninth heaviest Buteo in the world depending on what figures are used. However, in the northwestern United States, ferruginous hawk females are 35% heavier than female red-tails from the same area. [2] On average, western red-tailed hawks are relatively longer winged and lankier proportioned but are slightly less stocky, compact and heavy than eastern red-tailed hawks in North America. Eastern hawks may also have mildly larger talons and bills than western ones. Based on comparisons of morphology and function amongst all accipitrids, these features imply that western red-tails may need to vary their hunting more frequently to on the wing as the habitat diversifies to more open situations and presumably would hunt more variable and faster prey, whereas the birds of the east, which was historically well-wooded, are more dedicated perch hunters and can take somewhat larger prey but are likely more dedicated mammal hunters. [9] [32] [33] In terms of size variation, red-tailed hawks run almost contrary to Bergmann's rule (i.e. that northern animals should be larger in relation than those closer to the Equator within a species) as one of the northernmost subspecies, B. j. alascensis, is the second smallest race based on linear dimensions and that two of the most southerly occurring races in the United States, B. j. fuertesi and B. j. umbrinus, respectively, are the largest proportioned of all red-tailed hawks. [9] [33] [34] Red-tailed hawks tend have a relatively short but broad tails and thick, chunky wings. [30] Although often described as long-winged, [2] [4] the proportional size of the wings is quite small and red-tails have high wing loading for a buteonine hawk. For comparison, two other widespread Buteo hawks in North America were found to weigh: 30 g (1.1 oz) for every square centimeter of wing area in the rough-legged buzzard (B. lagopus) and 44 g (1.6 oz)/cm 2 in the red-shouldered hawk (B. lineatus). In contrast, the red-tailed hawk weighed considerably more for their wing area: 199 g (7.0 oz) per square cm. [35]

As is the case with many raptors, the red-tailed hawk displays sexual dimorphism in size, as females are on average 25% larger than males. [31] As is typical in large raptors, frequently reported mean body mass for red-tailed hawks is somewhat higher than expansive research reveals. [36] Part of this weight variation is seasonal fluctuations hawks tend to be heavier in winter than during migration or especially during the trying summer breeding season, and also due to clinal variation. Furthermore, immature hawks are usually lighter in mass than their adult counterparts despite having somewhat longer wings and tails. Male red-tailed hawks may weigh from 690 to 1,300 g (1.52 to 2.87 lb) and females may weigh 801 to 1,723 g (1.766 to 3.799 lb) (the lowest figure from a migrating female immature from Goshute Mountains, Nevada, the highest from a wintering female in Wisconsin). [5] [16] [37] Some sources claim the largest females can weigh up to 2,000 g (4.4 lb), but whether this is in reference to wild hawks (as opposed to those in captivity or used for falconry) is not clear. [38] The largest known survey of body mass in red-tailed hawks is still credited to Craighead and Craighead (1956), who found 100 males to average 1,028 g (2.266 lb) and 108 females to average 1,244 g (2.743 lb). However, these figures were apparently taken from labels on museum specimens, from natural history collections in Wisconsin and Pennsylvania, without note to the region, age, or subspecies of the specimens. [5] [39] However, 16 sources ranging in sample size from the aforementioned 208 specimens to only four hawks in Puerto Rico (with 9 of the 16 studies of migrating red-tails), showed that males weigh a mean of 860.2 g (1.896 lb) and females weigh a mean of 1,036.2 g (2.284 lb), about 15% lighter than prior species-wide published weights. Within the continental United States, typical weights of males can range from 840.8 g (1.854 lb) (for migrating males in Chelan County, Washington) to 1,031 g (2.273 lb) (for male hawks found dead in Massachusetts), and females ranged from 1,057.9 g (2.332 lb) (migrants in the Goshutes) to 1,373 g (3.027 lb) (for females diagnosed as B. j. borealis in western Kansas). [36] [9] [32] [40] [41] [42] [43] [44] Size variation in body mass reveals that the red-tailed hawk typically varies only a modest amount and that size differences are geographically inconsistent. Racial variation in average weights of great horned owls (Bubo virginianus) show that mean body mass is nearly twice (the heaviest race is about 36% heavier than the lightest known race on average) as variable as that of the hawk (where the heaviest race is only just over 18% heavier on average than the lightest). Also, great horned owls correspond well at the species level with Bergmann's rule. [9] [40]

Male red-tailed hawks can measure 45 to 60 cm (18 to 24 in) in total length, females measuring 48 to 65 cm (19 to 26 in) long. Their wingspan typically can range from 105 to 141 cm (3 ft 5 in to 4 ft 8 in), although the largest females may possible span up to 147 cm (4 ft 10 in). In the standard scientific method of measuring wing size, the wing chord is 325.1–444.5 mm (12.80–17.50 in) long. The tail measures 188 to 258.7 mm (7.40 to 10.19 in) in length. [2] [16] [45] The exposed culmen was reported to range from 21.7 to 30.2 mm (0.85 to 1.19 in) and the tarsus averaged 74.7–95.8 mm (2.94–3.77 in) across the races. [36] [9] [46] The middle toe (excluding talon) can range from 38.3 to 53.8 mm (1.51 to 2.12 in), with the hallux-claw (the talon of the rear toe, which has evolved to be the largest in accipitrids) measuring from 24.1 to 33.6 mm (0.95 to 1.32 in) in length. [36] [9]

Identification Edit

Although they overlap in range with most other American diurnal raptors, identifying most mature red-tailed hawks to species is relatively straightforward, particularly if viewing a typical adult at a reasonable distance. The red-tailed hawk is the only North American hawk with a rufous tail and a blackish patagium marking on the leading edge of its wing (which is obscured only on dark morph adults and Harlan’s hawks by similarly dark-colored feathers). [2] Other larger adult Buteo spp. in North America usually have obvious distinct markings that are absent in red-tails, whether the rufous-brown "beard" of Swainson's hawks (B. swainsonii) or the colorful rufous belly and shoulder markings and striking black-and-white mantle of red-shouldered hawks (also the small "windows" seen at the end of their primaries). [47] In perched individuals, even as silhouettes, the shape of large Buteo spp. may be distinctive, such as the wingtips overhanging the tail in several other species, but not in red-tails. North American Buteo spp. range from the dainty, compact builds of much smaller ones, such as broad-winged hawk (B. platypterus) to the heavyset, neckless look of ferruginous hawks or the rough-legged buzzards, which have a compact, smaller appearance than a red-tail in perched birds due to its small bill, short neck, and much shorter tarsi, while the opposite effect occurs in flying rough-legs with their much bigger wing area. [2] [47] In flight, most other large North American Buteo spp. are distinctly longer and more slender-winged than red-tailed hawks, with the much paler ferruginous hawk having peculiarly slender wings in relation to its massive, chunky body. Swainson's hawks are distinctly darker on the wing and ferruginous hawks are much paler-winged than typical red-tailed hawks. Pale morph adult ferruginous hawk can show mildly tawny-pink (but never truly rufous) upper tail, and like red-tails tend to have dark markings on underwing-coverts and can have a dark belly band, but compared to red-tailed hawks have a distinctly broader head, their remiges are much whiter looking with very small, dark primary tips, they lack the red-tail's diagnostic patagial marks and usually also lack the dark subterminal tail-band, and ferruginous hawks have totally feathered tarsi. With its whitish head, the ferruginous hawk is most similar to Krider's red-tailed hawks, especially in immature plumage, but the larger hawk has broader head and narrower wing shape, and the ferruginous immatures are paler underneath and on their legs. Several species share a belly band with the typical red-tailed hawk, but they vary from subtle (as in the ferruginous hawk) to solid blackish, the latter in most light-morph rough-legged buzzards. [2] [27] More difficult to identify among adult red-tails are their darkest variations, as most species of Buteo in North America also have dark morphs. Western dark morph red-tails (i.e. B. j. calurus) adults, however, retain the typical distinctive brick-red tail, which other species lack, and may stand out even more against the otherwise all chocolate-brown to black bird. Standard pale juveniles when perched show a whitish patch in the outer half of the upper surface of the wing, which other juvenile Buteo spp. lack. [4] The most difficult to identify stages and plumage types are dark morph juveniles, Harlan's hawk and some Krider's hawks (the latter mainly with typical ferruginous hawks as mentioned). Some darker juveniles are similar enough to other Buteo juveniles that they "cannot be identified to species with any confidence under various field conditions." [5] [4] However, field identification techniques have advanced in the last few decades and most experienced hawk-watchers can distinguish even the most vexingly plumaged immature hawks, especially as the wing shapes of each species becomes apparent after seeing many. Harlan’s hawks are most similar to dark morph rough-legged buzzards and dark morph ferruginous hawks. Wing shape is the most reliable identification tool for distinguishing Harlan's hawks from these, but also the pale streaking on the breast of Harlan's, which tends to be conspicuous in most individuals, and is lacking in the other hawks. Also, dark morph ferruginous hawks do not have the dark subterminal band of a Harlan's hawk, but do bear a black undertail covert lacking in Harlan's. [2] [48]

Vocalization Edit

The cry of the red-tailed hawk is a 2- to 3-second, hoarse, rasping scream, variously transcribed as kree-eee-ar, tsee-eeee-arrr or sheeeeee, [49] that begins at a high pitch and slurs downward. [2] [27] [50] This cry is often described as sounding similar to a steam whistle. [31] [27] The red-tailed hawk frequently vocalizes while hunting or soaring, but vocalizes loudest and most persistently in defiance or anger, in response to a predator or a rival hawk's intrusion into its territory. [27] [49] At close range, it makes a croaking guh-runk, possibly as a warning sound. [51] Nestlings may give peeping notes with a "soft, sleepy quality" that give way to occasional screams as they develop, but those are more likely to be a soft whistle rather than the harsh screams of the adults. Their latter hunger call, given from 11 days (as recorded in Alaska) to after fledgling (in California), is different, a two-syllabled, wailing klee-uk food cry exerted by the young when parents leave the nest or enter their field of vision. [5] [52] A strange mechanical sound "not very unlike the rush of distant water" has been reported as uttered in the midst of a sky-dance. [5] A modified call of chirp-chwirk is given during courtship, while a low key, duck-like nasal gank may be given by pairs when they are relaxed. [27]

The fierce, screaming cry of the adult red-tailed hawk is frequently used as a generic raptor sound effect in television shows and other media, even if the bird featured is not a red-tailed hawk. [53] [54] It is especially used in depictions of the bald eagle, which contributes to the common misconception that it is a bald eagle cry actual bald eagle vocalizations are far softer and more chirpy than those of a red-tailed hawk. [55]

The red-tailed hawk is one of the most widely distributed of all raptors in the Americas. It occupies the largest breeding range of any diurnal raptor north of the Mexican border, just ahead of the American kestrel (Falco sparverius). While the peregrine falcon (Falco peregrinus) has a greater latitudinal distribution as a nester in North America, its range as a breeding species is far more sporadic and sparse than that of red-tailed hawks. [56] The red-tailed hawk breeds from nearly north-central Alaska, the Yukon, and a considerable portion of the Northwest Territories, there reaching as far as a breeder as Inuvik, Mackenzie River Delta and skirting the southern shores of Great Bear Lake and Great Slave Lake. Thereafter in northern Canada, breeding red-tails continue to northern Saskatchewan and across to north-central Ontario east to central Quebec and the Maritime Provinces of Canada, and south continuously to Florida. No substantial gaps occur throughout the entire contiguous United States, where breeding red-tailed hawks do not occur. Along the Pacific, their range includes all of Baja California, including Islas Marías, and Socorro Island in the Revillagigedo Islands. On the mainland, breeding red-tails are found continuously to Oaxaca, then experience a brief gap at the Isthmus of Tehuantepec thereafter subsequently continuing from Chiapas through central Guatemala on to northern Nicaragua. To the south, the population in highlands from Costa Rica to central Panama is isolated from breeding birds in Nicaragua. Further east, breeding red-tailed hawks occur in the West Indies in north Bahamas (i.e. Grand Bahama, Abaco and Andros) and all larger islands (such as Cuba, Jamaica, Hispaniola, and Puerto Rico) and into the northern Lesser Antilles (Virgin Islands, Saint Barthélemy, Saba, Saint Kitts, and Nevis, being rare as a resident on Saint Eustatius and are probably extinct on Saint Martin). Their typical winter range stretches from southern Canada south throughout the remainder of the breeding range. [2] [57] [56]

Red-tailed hawks have shown the ability to become habituated to almost any habitat present in North and Central America. Their preferred habitat is mixed forest and field, with trees or alternately high bluffs that may be used as nesting and perching sites. They occupy a wide range of habitats and altitudes, including deserts, grasslands, nearly any coastal or wetland habitat, mountains, foothills, coniferous and deciduous woodlands, and tropical rainforests. Agricultural fields and pastures, which are more often than not varied with groves, ridges, or streamside trees in most parts of America, may make nearly ideal habitat for breeding or wintering red-tails. [1] [5] [9] [27] Some red-tails may survive or even flourish in urban areas, usually hunting and roosting in available urban parks, cemeteries, road verges, and so on, and nesting freely either in trees or man-made structures. [49] [58] One famous urban red-tailed hawk, known as "Pale Male", became the subject of a nonfiction book, Red-Tails in Love: A Wildlife Drama in Central Park, and is the first known red-tail in decades to successfully nest and raise young in the crowded New York City borough of Manhattan. [59] [60] [61] [62] As studied in Syracuse, New York, the highway system has been very beneficial to red-tails as it juxtaposed trees and open areas and blocks human encroachment with fences, with the red-tailed hawks easily becoming acclimated to car traffic. The only practice that has a negative effect on the highway-occupying red-tails is the planting of exotic Phragmites, which may occasionally obscure otherwise ideal highway habitat. [63]

In the northern Great Plains, the widespread practices of wildfire suppression and planting of exotic trees by humans has allowed groves of aspen and various other trees to invade what was once vast, almost continuous prairie grasslands, causing grassland obligates such as ferruginous hawks to decline and allowing parkland-favoring red-tails to flourish. [5] [64] To the contrary, clear-cutting of mature woodlands in New England, resulting in only fragmented and isolated stands of trees or low second growth remaining, was recorded to also benefit red-tailed hawks, despite being to the determent of breeding red-shouldered hawks. [65] The red-tailed hawk, as a whole, rivals the peregrine falcon and the great horned owl among raptorial birds in the use of diverse habitats in North America. [5] [66] Beyond the high Arctic (as they discontinue as a breeder at the tree line), few other areas exist where red-tailed hawks are absent or rare in North and Central America. Some areas of unbroken forest, especially lowland tropical forests, rarely host red-tailed hawks, although they can occupy forested tropical highlands surprisingly well. In deserts, they can only occur where some variety of arborescent growth or ample rocky bluffs or canyons occur. [28] [67] [68]

The red-tailed hawk is highly conspicuous to humans in much of its daily behavior. Most birds in resident populations, which are well more than half of all red-tailed hawks, usually split nonbreeding-season activity between territorial soaring flight and sitting on a perch. Often, perching is for hunting purposes, but many sit on a tree branch for hours, occasionally stretching on a single wing or leg to keep limber, with no signs of hunting intent. [5] [4] [65] Wintering typical pale-morph hawks in Arkansas were found to perch in open areas near the top of tall, isolated trees, whereas dark morphs more frequently perched in dense groups of trees. [4] For many, and perhaps most, red-tailed hawks being mobbed by various birds is a daily concern and can effectively disrupt many of their daily behaviors. Mostly larger passerines, of multiple families from tyrant flycatchers to icterids, mob red-tails, despite other raptors, such as Accipiter hawks and falcons, being a notably greater danger to them. [69] [70] The most aggressive and dangerous attacker as such is likely to be various crows or other corvids, i.e. American crows (Corvus brachyrhynchos), because a mobbing group (or "murder") of them can number up to as many as 75 crows, which may cause grievous physical harm to a solitary hawk, and if the hawks are nesting, separate the parent hawks and endanger the eggs or nestlings within their nest to predation by crows. [71] [72] Birds that mob red-tailed hawks can tell how distended the hawk's crop is (i.e. the upper chest and throat area being puffy versus flat-feathered and sleek), thus mob more often when the hawk is presumably about to hunt. [73]

Flight Edit

In flight, this hawk soars with wings often in a slight dihedral, flapping as little as possible to conserve energy. Soaring is by far the most efficient method of flight for red-tailed hawks, so is used more often than not. [74] Active flight is slow and deliberate, with deep wing beats. Wing beats are somewhat less rapid in active flight than in most other Buteo hawks, even heavier species such as ferruginous hawks tend to flap more swiftly, due to the morphology of the wings. [75] In wind, it occasionally hovers on beating wings and remains stationary above the ground, but this flight method is rarely employed by this species. [9] [28] When soaring or flapping its wings, it typically travels from 32 to 64 km/h (20 to 40 mph), but when diving may exceed 190 km/h (120 mph). [50] Although North American red-tailed hawks will occasionally hunt from flight, a great majority of flight by red-tails in this area is for non-hunting purpose. [74] During nest defense, red-tailed hawks may be capable of surprisingly swift, vigorous flight, while repeatedly diving at perceived threats. [76]

Migration Edit

Red-tailed hawks are considered partial migrants, as in about the northern third of their distribution, which is most of their range in Canada and Alaska, they almost entirely vacate their breeding grounds. [2] [9] In coastal areas of the north, however, such as in the Pacific Northwest to southern Alaska and in Nova Scotia on the Atlantic, red-tailed hawks do not usually migrate. [5] More or less, any area where snow cover is nearly continuous during the winter shows an extended absence of most red-tailed hawks, so some areas as far south as Montana may show strong seasonal vacancies of red-tails. [5] In southern Michigan, immature red-tailed hawks tended to remain in winter only when voles were abundant. During relatively long, harsh winters in Michigan, many more young ones were reported in northeastern Mexico. [5] [39] To the opposite extreme, hawks residing as far north as Fairbanks, Alaska, may persevere through the winter on their home territory, as was recorded with one male over three consecutive years. [77] Birds of any age tend to be territorial during winter but may shift ranges whenever food requirements demand it. [5] Wintering birds tend to perch on inconspicuous tree perches, seeking shelter especially if they have a full crop or are in the midst of poor or overly windy weather. Adult wintering red-tails tend to perch more prominently than immatures do, which select lower or more secluded perches. Immatures are often missed in winter bird counts, unless they are being displaced by dominant adults. Generally, though, immatures can seem to recognize that they are less likely to be attacked by adults during winter and can perch surprisingly close to them. Age is the most significant consideration of wintering hawks' hierarchy, but size does factor in, as larger immatures (presumably usually females) are less likely to displaced than smaller ones. [4] [5] [9] Dark adult red-tailed hawks appear to be harder to locate when perched than other red-tails. In Oklahoma, for example, wintering adult Harlan's hawks were rarely engaged in fights or chased by other red-tails. These hawks tended to gather in regional pockets and frequently the same ones occurred year-to-year. [77] In general, migratory behavior is complex and reliant on each individual hawk's decision-making (i.e. whether prey populations are sufficient to entice the hawk to endure prolonged snow cover). [9] During fall migration, departure may occur as soon as late September, but peak movements occur in late October and all of November in the United States, with migration ceasing after mid-December. The northernmost migrants may pass over resident red-tailed hawks in the contiguous United States, while the latter are still in the midst of brooding fledglings. [5] Not infrequently, several autumn hawk watches in Ontario, Quebec, and the northern United States record 4,500–8,900 red-tailed hawks migrating through each fall, with records of up to 15,000 in a season at Hawk Ridge hawk watch in Duluth, Minnesota. [2] [78] Unlike some other Buteo spp., such as [wainson's hawks and broad-winged hawks (B. platypterus), red-tailed hawks do not usually migrate in groups, instead passing by one-by-one, and only migrate on days when winds are favorable. [2] [5] Most migrants do not go past southern Mexico in late autumn, but a few may annually move as far south as breeding red-tailed hawks in Panama. However, a few records were made of wintering migrant red-tails turning up in Colombia, the first records of the species in that country or anywhere in South America. [2] [9] [79] Spring northward movements may commence as early as late February, with peak numbers usually occurring in late March and early April. Seasonal counts may include up to 19,000 red-tails in spring at Derby Hill hawk watch, in Oswego, New York, sometimes more than 5,000 are recorded in a day there. [2] [80] The most northerly migratory individuals may not reach breeding grounds until June, even adults. [2] [77]

Immature hawks migrate later than adults in spring on average, but not, generally speaking, in autumn. In the northern Great Lakes, immatures return in late May to early June, when adults are already well into their nesting season and must find unoccupied ranges. [5] In Alaska, adults tend to migrate before immatures in early to mid-September, to the contrary of other areas, probably as heavy snowfall begins. [77] [81] Yearlings that were banded in southwestern Idaho stayed for about 2 months after fledging, and then traveled long distances with a strong directional bias, with 9 of 12 recovered southeast of the study area- six of these moved south to coastal lowlands in Mexico] and as far as Guatemala, 4,205 km (2,613 mi) from their initial banding. [82] In California, 35 hawks were banded as nestlings 26 were recovered at less than 50 miles away, with multidirectional juvenile dispersals. Nestlings banded in Southern California sometimes actually traveled north as far as 1,190 km (740 mi) to Oregon, ranging to the opposite extreme as far as a banded bird from the Sierra Nevadas that moved 1,700 km (1,100 mi) south to Sinaloa. [5] [83] Nestlings banded in Green County, Wisconsin, did not travel very far comparatively by October–November, but by December, recoveries were found in states including Illinois, Iowa, Texas, Louisiana, and Florida. [84]

The red-tailed hawk is carnivorous, and a highly opportunistic feeder. Nearly any small animal they encounter may be viewed as potential food. [4] Their most common prey are small mammals such as rodents and lagomorphs, but they also consume birds, reptiles, fish, amphibians, and invertebrates. Prey varies considerably with regional and seasonal availability, but usually centers on rodents, accounting for up to 85% of a hawk's diet. [31] In total, nearly 500 prey species have been recorded in their diet, almost as many as great horned owls have been recorded as taking. [9] [65] [85] [86] When 27 North American studies are reviewed, mammals make up 65.3% of the diet by frequency, 20.9% by birds, 10.8% by reptiles, 2.8% by invertebrates, and 0.2% by amphibians and fish. [5] [4] [85] [86] The geometric mean body mass of prey taken by red-tailed hawks in North America is about 187 g (6.6 oz) based on a pair of compilation studies from across the continent, regionally varying at least from 43.4 to 361.4 g (1.53 to 12.75 oz). [87] [88] Staple prey (excluding invertebrates) has been claimed to weigh from 15 to 2,114 g (0.033 to 4.661 lb), ranging roughly from the size of a small mouse or lizard to the size of a black-tailed jackrabbit (Lepus californicus). [5] [9] [89] The daily food requirements range from 7 to 11.2% of their own body weight, so that about three voles or the equivalent weight are required daily for a typical range adult. [39]

The talons and feet of red-tailed hawks are relatively large for a Buteo hawk in an average-sized adult red-tail, the "hallux-claw" or rear talon, the largest claw on all accipitrids, averages about 29.7 mm (1.17 in). [32] [90] In fact, the talons of red-tails in some areas averaged of similar size to those of ferruginous hawks which can be considerably heavier and notably larger than those of the only slightly lighter Swainson's hawk. [32] [91] [92] This species may exert an average of about 91 kg/cm 2 (1,290 lbf/in 2 ) of pressure through its feet. [32] [93] [94] Owing to its morphology, red-tailed hawks generally can attack larger prey than other Buteo hawks typically can, and are capable of selecting the largest prey of up to their own size available at the time of hunting, though in all likelihood numerically most prey probably weighs about 20% of the hawk's own weight (as is typical of many birds of prey). [9] [39] [95] Red-tailed hawks usually hunt by watching for prey activity from a high perch, also known as still hunting. Upon being spotted, prey is dropped down upon by the hawk. Red-tails often select the highest available perches within a given environment, since the greater the height they are at, the less flapping is required and the faster the downward glide they can attain toward nearby prey. If prey is closer than average, the hawk may glide at a steep downward angle with few flaps, if farther than average, it may flap a few swift wingbeats alternating with glides. Perch hunting is the most successful hunting method generally speaking for red-tailed hawks and can account for up to 83% of their daily activities (i.e. in winter). [9] [5] [96] Wintering pairs may hunt together and aseasonally may join together to group hunt agile prey that they may have trouble catching by themselves, such as tree squirrels. This may consist of stalking opposites sides of a tree, to surround the squirrel and almost inevitably drive the rodent to be captured by one after being flushed by the other hawk. [5] [27]

The most common flighted hunting method for red-tail is to cruise around 10 to 50 m (33 to 164 ft) over the ground with flap-and-glide type flight, interspersed occasionally with harrier-like quarters over the ground. This method is less successful than perch hunting, but seems relatively useful for capturing small birds and may be show the best results while hunting in hilly country. [2] [5] [27] Hunting red-tailed hawks readily use trees, bushes, or rocks for concealment before making a surprise attack, even showing a partial ability to dodge among trees in an Accipiter-like fashion. Among thick stands of spruce in Alaska, a dodging hunting flight was thought to be unusually important to red-tails living in extensive areas of conifers, with hawks even coming to the ground and walking hurriedly in prey pursuit especially if the prey was large, a similar behavior to goshawks. [5] [77] Additional surprisingly swift aerial hunting has reported in red-tails that habitually hunt bats in Texas. Here, the bat-hunting specialists stooped with half-closed wings, quite falcon-like, plowing through the huge stream of bats exiting their cave roosts, then zooming upwards with a bat in its talons. These hawks also flew parallel closely to the stream, then veer sharply into it and seize a bat. [97] [98] [99] In the neotropics, red-tails have shown the ability to dodge amongst forest canopy whilst hunting. [2] [100] In Kansas, red-tailed hawks were recorded sailing to catch flying insects, a hunting method more typical of a Swainson's hawk. [101] Alternately, they may drop to the ground to forage for insects like grasshoppers and beetles as well as other invertebrates and probably amphibians and fish (except by water in the latter cases). Hunting afoot seems to be particularly prevalent among immatures. Young red-tailed hawks in northeastern Florida were recorded often extracting earthworms from near the surface of the ground and some had a crop full of earthworms after rains. Ground hunting is also quite common on Socorro Island, where no native land mammals occur, and invertebrates are more significant to their overall diet. [2] [5] [102] A red-tailed hawk was observed to incorporate an unconventional killing method, which was drowning a heron immediately after capture. [103] One red-tailed hawk was seen to try to grab a young ground squirrel and, upon missing it, screamed loudly, which in turn caused another young squirrel to break into a run, wherein it was captured. Whether this was an intentional hunting technique needs investigation. [27] Upon capture, smaller prey is taken to a feeding perch, which is almost always lower than a hunting perch. Among small prey, rodents are often swallowed whole, as are shrews and small snakes, while birds are plucked and beheaded. Even prey as small as chipmunks may take two or three bites to consume. Larger mammals of transportable size are at times beheaded and have part of their fur discarded, then leftovers are either stored in a tree or fall to the ground. Large prey, especially if too heavy to transport on the wing, is often dragged to a secluded spot and dismantled in various ways. If they can successfully carry what remains to a low perch, they tend to feed until full and then discard the rest. [5] [4] [27]

Mammals Edit

Rodents are certainly the type of prey taken most often by frequency, but their contribution to prey biomass at nests can be regionally low, and the type, variety and importance of rodent prey can be highly variable. In total, well over 100 rodent species have turned up the diet of red-tailed hawks. [9] [85] [86] Rodents of extremely varied sizes may be hunted by red-tails, with species ranging in size from the 8.2 g (0.29 oz) eastern harvest mouse (Reithrodontomys humulis) to marmots (Marmota ssp.), weighing some 3,300 g (7.3 lb) in spring, although whether they can take full grown marmots is questionable. At least some attacks on adult marmots like groundhogs (Marmota monax) are abortive. [104] [105] [106] At times, the red-tailed hawk is thought of as a semi-specialized vole-catcher, but voles are a subsistence food that are more or less are taken until larger prey can be captured. In an area of Michigan, immature hawks took almost entirely voles but adults were diversified feeders. [5] [39] Indeed, the 44.1 g (1.56 oz) meadow vole (Microtus pennsylvanicus) was the highest frequency prey species in 27 dietary studies across North America, accounting for up to 54% of the food at nests by frequency. It is quite rare for any one species to make up more than half of the food at any dietary study for red-tailed hawks. [5] [4] [85] [86] [107] [108] In total about 9 Microtus species are known in the overall diet, with 5 other voles and lemmings known to be included in their prey spectrum. [85] [86] Another well-represented species was the 27.9 g (0.98 oz) prairie vole (Microtus ochrogaster), which were the primary food, making up 26.4% of a sample of 1322, in eastern Kansas. [109] While crepuscular in primary feeding activity, voles are known to be active both day and night, and so are reliable food for hawks than most non-squirrel rodents, which generally are nocturnal in activity. [39] [110] [111] Indeed, most other microtine rodents are largely inaccessible to red-tailed hawks due to their strongly nocturnal foraging patterns, even though 24 species outside of voles and lemmings are known to be hunted. Woodrats are taken as important supplemental prey in some regions, being considerably larger than most other crictetid rodents, and some numbers of North American deermouse (Peromyscus maniculatus) may turn up. The largest representation of the latter species was contributing 11.9% of the diet in the Great Basin of Utah, making them the second best represented prey species there. [85] [112] Considering this limited association with nocturnal rodents, the high importance of pocket gophers in the diet of red-tailed hawks is puzzling to many biologists, as these tend to be highly nocturnal and elusive by day, rarely leaving the confines of their burrow. At least 8 species of pocket gopher are included in the prey spectrum (not to mention 5 species of pocket mice). The 110 g (3.9 oz) northern pocket gopher (Thomomys talpoides) is particularly often reported and, by frequency, even turns up as the third most often recorded prey species in 27 American dietary studies. Presumably, hunting of pocket gophers by red-tails, which has possibly never been witnessed, occurs in dim light at first dawn and last light of dusk when they luck upon a gopher out foraging. [5] [85] [86] [113] [114]

By far, the most important prey among rodents are squirrels, as they are almost fully diurnal. All told, nearly 50 species from the squirrel family have turned up as food. In particular, where they are distributed, ground squirrels are doubly attractive as a primary food source due to their ground dwelling habits, as red-tails prefer to attack prey that is terrestrial. [9] [5] [85] [86] There are also many disadvantages to ground squirrels as prey: they can escape quickly to the security of their burrows, they tend to be highly social and they are very effective and fast in response to alarm calls, and a good deal of species enter hibernation that in the coldest climates can range up to a 6 to 9-month period (although those in warmer climates with little to no snowy weather often have brief dormancy and no true hibernation). Nonetheless, red-tailed hawks are devoted predators of ground squirrels, especially catching incautious ones as they go out foraging (which more often than not are younger animals). [115] [116] [117] [118] A multi-year study conducted on San Joaquin Experimental Range in California, seemingly still the largest food study to date done for red-tailed hawks with 4031 items examined, showed that throughout the seasons the 722 g (1.592 lb) California ground squirrel (Otospermophilus beecheyi) was the most significant prey, accounting for 60.8% of the breeding season diet and about 27.2% of the diet for hawks year-around. Because of the extremely high density of red-tailed hawks on this range, some pairs came to specialize on diverse alternate prey, which consisted variously of kangaroo rats, lizards, snakes or chipmunks. One pair apparently lessened competition by focusing on pocket gophers instead despite being near the center of ground squirrel activity. [119] [120] In Snake River NCA, the primary food of red-tailed hawks was the 203.5 g (7.18 oz) Townsend's ground squirrel (Urocitellus townsendii), which made up nearly 21% of the food in 382 prey items across several years despite sharp spikes and crashes of the ground squirrel population there. [89] [121] The same species was the main food of red-tailed hawks in southeastern Washington, making up 31.2% of 170 items. [122] An even closer predatory relationship was reported in the Centennial valley of Montana and south-central Montana, where 45.4% of 194 prey items and 40.2% of 261 items, respectively, of the food of red-tails consisted of the 455.7 g (1.005 lb) Richardson's ground squirrel (Urocitellus richardsonii). [91] [123] [124] Locally in Rochester, Alberta, Richardson's ground squirrel, estimated to average 444 g (15.7 oz), were secondary in number to unidentified small rodents but red-tails in the region killed an estimated 22–60% of the area’s ground squirrel, a large dent in the squirrel’s population. [125] Further east, ground squirrels are not so reliably distributed, but one study in southern Wisconsin, in one of several quite different dietary studies in that state, the 172.7 g (6.09 oz) thirteen-lined ground squirrel (Ictidomys tridecemlineatus) was the main prey species, making up 29.7% of the diet (from a sample of 165). [126] [127]

In Kluane Lake, Yukon, 750 g (1.65 lb) Arctic ground squirrels (Spermophilus parryii) were the main overall food for Harlan’s red-tailed hawks, making up 30.8% of a sample of 1074 prey items. When these ground squirrels enter their long hibernation, the breeding Harlan’s hawks migrate south for the winter. [128] Nearly as important in Kluane Lake was the 200 g (7.1 oz) American red squirrel (Tamiasciurus hudsonicus), which constituted 29.8% of the above sample. Red squirrels are highly agile dwellers on dense spruce stands, which has caused biologists to ponder how the red-tailed hawks are able to routinely catch them. It is possible that the hawks catch them on the ground such as when squirrels are digging their caches, but theoretically the dark color of the Harlan’s hawks may allow them to more effectively ambush the squirrels within the forests locally. [5] [127] [128] While American red squirrel turn up not infrequently as supplementary prey elsewhere in North America, other tree squirrels seem to be comparatively infrequently caught, at least during the summer breeding season. It is known that pairs of red-tailed hawks will cooperative hunt tree squirrels at times, probably mostly between late fall and early spring. Fox squirrels (Sciurus niger), the largest of North America’s tree squirrels at 800 g (1.8 lb), are fairly regular supplemental prey but the lighter, presumably more agile 533 g (1.175 lb) eastern gray squirrel (Sciurus carolinensis) appears to be seldom caught based on dietary studies. [9] [84] [126] [127] [129] While adult marmot may be difficult for red-tailed hawks to catch, young marmots are readily taken in numbers after weaning, such as a high frequency of yellow-bellied marmot (Marmota flaviventris) in Boulder, Colorado. [130] Another grouping of squirrels but at the opposite end of the size spectrum for squirrels, the chipmunks are also mostly supplemental prey but are considered more easily caught than tree squirrels, considering that they are more habitual terrestrial foragers. [5] [4] [85] In central Ohio, eastern chipmunks (Tamias striatus), the largest species of chipmunk at an average weight of 96 g (3.4 oz), were actually the leading prey by number, making up 12.3% of a sample of 179 items. [129] [131]

Outside of rodents, the most important prey for North American red-tailed hawks is rabbits and hares, of which at least 13 species are included in their prey spectrum. By biomass and reproductive success within populations, these are certain to be the most significant food source to the species (at least in North America). [9] [85] Adult Sylvilagus rabbits known to be hunted by red-tails can range from the 700 g (1.5 lb) brush rabbit (Sylvilagus bachmani) to the Tres Marias rabbit (Sylvilagus graysoni) at 1,470 g (3.24 lb) while all leporids hunted may range the 421.3 g (14.86 oz) pygmy rabbit (Brachylagus idahoensis) to hares and jackrabbits potentially up twice the hawk’s own weight. [132] [133] [134] [42] While primarily crepuscular in peak activity, rabbits and hares often foraging both during day and night and so face almost constant predatory pressure from a diverse range of predators. Male red-tailed hawks or pairs which are talented rabbit hunters are likely have higher than average productivity due to the size and nutrition of the meal ensuring healthy, fast-growing offspring. [5] [9] [39] [135] Most widely reported are the cottontails, which the three most common North America varieties softly grading into mostly allopatric ranges, being largely segregated by habitat preferences where they overlap in distribution. Namely, in descending order of reportage were: the eastern cottontail (Sylvilagus floridanus), the second most widely reported prey species overall in North America and with maximum percentage known in a given study was 26.4% in Oklahoma (out of 958 prey items), the mountain cottontail (Sylvilagus nuttallii), maximum representation being 17.6% out of a sample of 478 in Kaibab Plateau, Arizona and the desert cottontail (Sylvilagus audubonii), maximum representation being 22.4% out of a sample of 326 in west-central Arizona. [85] [123] [136] [137] Black-tailed jackrabbits (Lepus californicus) are even more intensely focused upon as a food source by the hawks found in the west, particularly the Great Basin. This species is likely the largest prey routinely hunted by red-tails and the mean prey size where jackrabbits are primarily hunted is indeed the highest known overall in the species. When jackrabbit numbers crash, red-tailed hawk productivity tends to decline synchronically. In northern Utah, black-tailed jackrabbits made up 55.3% by number of a sample of 329. Elsewhere, they are usually somewhat secondary by number. Mean sizes of jackrabbits taken can range up to approximately 2,114 g (4.661 lb), but probably quantitatively mostly juvenile and yearling jackrabbits are caught. Prime adult jackrabbits, with weights at times exceeding 2,700 g (6.0 lb), are difficult and taken infrequently, short of by particularly large and aggressive female red-tails. [85] [122] [89] [112] Other even larger species are sometimes taken as prey such as the white-tailed jackrabbit (Lepus townsendii), but whether this includes healthy adults, as they average over 3,200 g (7.1 lb), is unclear. [91]

In the boreal forests of Canada and Alaska, red-tails are fairly dependent on the snowshoe hare (Lepus americanus), falling somewhere behind the great horned owl and ahead of the northern goshawk in their regional reliance on this food source. [77] [128] [125] The hunting preferences of red-tails who rely on snowshoe hares is variable. In Rochester, Alberta, 52% of snowshoe hares caught were adults, such prey estimated to average 1,287 g (2.837 lb), and adults, in some years, were six times more often taken than juvenile hares, which averaged an estimated 560 g (1.23 lb). 1.9–7.1% of adults in the regional population of Rochester were taken by red-tails, while only 0.3–0.8 of juvenile hares were taken by them. Despite their reliance on it, only 4% (against 53.4% of the biomass) of the food by frequency here was made up of hares. [125] On the other hand, in Kluane Lake, Yukon, juvenile hares were taken roughly 11 times more often than adults, despite the larger size of adults here, averaging 1,406.6 g (3.101 lb), and that the overall prey base was less diverse at this more northerly clime. In both Rochester and Kluane Lake, the number of snowshoe hares taken was considerably lower than numbers of ground squirrels taken. The differences of average characteristics of snowshoe hares that were hunted may be partially due to habitat (extent of bog openings to dense forest) or topography. [128] [138] Another member of the Lagomorpha order has been found in the diet, the much smaller American pika (Ochotona princeps), at 150 g (5.3 oz), but is not quantitatively common in the foods of the species so far as is known. [139]

A diversity of mammals may be consumed opportunistically outside of the main food groups of rodents and leporids, but usually occur in low numbers. At least five species each are taken of shrews and moles, ranging in size from their smallest mammalian prey, the cinereus (Sorex cinereus) and least shrews (Cryptotis parva), which both weigh about 4.4 g (0.16 oz), to Townsend's mole (Scapanus townsendii), which weighs about 126 g (4.4 oz). [85] [86] [140] [141] [142] [143] A respectable number of the 90 g (3.2 oz) eastern mole (Scalopus aquaticus) were recorded in studies from Oklahoma and Kansas. [85] [109] Four species of bat have been recorded in their foods. [85] [119] The red-tailed hawks local to the large cave colonies of 12.3 g (0.43 oz) Mexican free-tailed bats (Tadarida brasiliensis) in Texas can show surprising agility, some of the same hawks spending their early evening and early morning hours in flight patrolling the cave entrances in order to stoop suddenly on these flighted mammals. [97] [98] [144] Larger miscellaneous mammalian prey are either usually taken as juveniles, like the nine-banded armadillo (Dasypus novemcinctus), or largely as carrion, like the Virginia opossum (Didelphis virginiana). [143] [145] Small carnivorans may be taken, usually consisting of much smaller mustelids, like the 150.6 g (5.31 oz) long-tailed weasel (Mustela frenata), which was surprisingly widely taken as a supplemental prey species. [100] [85] [89] [127] [146] Adult ringtails (Bassariscus astutus), which are about the same weight as a red-tailed hawk at 1,015 g (2.238 lb), are taken as prey occasionally. [136] Larger carnivoran remains are sometimes found amongst their foods, but most are likely taken as juveniles or smaller range adults, or otherwise consumed only as carrion. Some of the relatively larger carnivorans red-tailed hawks have been known to eat have included red fox ( Vulpes vulpes), kit fox (Vulpes macrotis), white-nosed coati (Nasua narica), raccoon (Procyon lotor), striped skunk (Mephitis mephitis) and domestic cats (Felis silvestris catus). [86] [130] [147] [148] [149] A red-tailed hawk was filmed killing a small cat in a city area. [150] Many of these medium-sized carnivorans are probably visited as roadkill, especially during the sparser winter months, but carrion has turned up more widely than previously thought. Some nests have been found (to the occasional "shock" of researchers) with body parts from large domestic stock like sheep (Ovis aries), pigs (Sus scrofa domesticus), horses (Equus caballus ferus) and cattle (Bos primigenius taurus) (not to mention wild varieties like deer), which red-tails must visit when freshly dead out on pastures and take a couple talonfuls of meat. [5] [136] [119] [147] In one instance, a red-tailed hawk was observed to kill a small but seemingly healthy lamb. These are born heavier than most red-tails at 1,500 g (3.3 lb) but in this instance, the hawk was scared away before it could consume its kill by the rifle fire of the shepherd who witnessed the instance. [151]

Birds Edit

Like most (but not all) Buteo hawks, red-tailed hawks do not primarily hunt birds in most areas, but can take them fairly often whenever they opportune upon some that are vulnerable. Birds are, by far, the most diverse class in the red-tailed hawk’s prey spectrum, with well over 200 species known in their foods. [65] [85] [86] In most circumstances where birds become the main food of red-tailed hawks, it is in response to ample local populations of galliforms. As these are meaty, mostly terrestrial birds which usually run rather than fly from danger (although all wild species in North America are capable of flight), galliforms are ideal avian prey for red-tails. Some 23 species of galliforms are known to be taken by red-tailed hawks, about a third of these being species introduced by humans. [85] [86] Native quails of all five North American species may expect occasional losses. [119] [152] [153] All 12 species of grouse native to North America are also occasionally included in their prey spectrum. [128] [91] [154] [155] [156] [157] [158] [159] [160] In the state of Wisconsin, two large studies, from Waupun and Green County, found the main prey species to be the ring-necked pheasant (Phasianus colchicus), making up 22.7% of a sample of 176 and 33.8% of a sample of 139, respectively. [84] [161] With a body mass averaging 1,135 g (2.502 lb), adult pheasants are among the largest meals that male red-tails are likely to deliver short of adult rabbits and hares and therefore these nests tend to be relatively productive. Despite being not native to North America, pheasants usually live in a wild state. All Wisconsin studies also found large numbers of chickens (Gallus gallus domesticus), making up as much as 14.4% of the diet. Many studies reflect that free-ranging chickens are vulnerable to red-tailed hawks although somewhat lesser numbers are taken by them overall in comparison to nocturnal predators (i.e. owls and foxes) and goshawks. [84] [88] [161] In Rochester, Alberta, fairly large numbers of ruffed grouse (Bonasa umbellus) were taken but relatively more juveniles were taken of this species than the two other main contributors to biomass here, snowshoe hare and Townsend’s ground squirrel, as they are fairly independent early on and more readily available. Here the adult grouse was estimated to average 550 g (1.21 lb) against the average juvenile which in mid-summer averaged 170 g (6.0 oz). [125]

Beyond galliforms, three other quite different families of birds make the most significant contributions to the red-tailed hawk’s avian diet. None of these three families are known as particularly skilled or swift fliers but the species are generally small enough that they would generally easily be more nimble in flight than a red-tailed hawk. One of these are the woodpeckers, if only for one species, the 131.6 g (4.64 oz) northern flicker (Colaptes auratus), which was the best represented bird species in the diet in 27 North American studies and was even the fourth most often detected prey species of all. [5] [4] [85] [86] Woodpeckers are often a favorite in the diet of large raptors as their relatively slow, undulating flight makes these relatively easy targets. The flicker in particular is a highly numerous species that has similar habitat preferences to red-tailed hawks, preferring fragmented landscapes with trees and openings or parkland-type wooded mosaics, and often forage on the ground for ants, which may make them even more susceptible. [162] [163] Varied other woodpecker species may turn up in their foods, from the smallest to the largest extant in North America, but are much more infrequently detected in dietary studies. [143] [164] Another family relatively often selected prey family are corvids, which despite their relatively large size, formidable mobbing abilities and intelligence are also slower than average fliers for passerines. 14 species of corvid are known to fall prey to red-tailed hawks. [85] [86] [165] In the Kaibab Plateau, the 128 g (4.5 oz) Steller's jay (Cyanocitta stelleri) were the fourth most identified prey species (10.3% of the diet). [136] 453 g (0.999 lb) American crows are also regularly detected supplemental prey in several areas. [84] [123] [161] Even the huge common raven (Corvus corax), at 1,050 g (2.31 lb) at least as large as red-tailed hawk itself, may fall prey to red-tails, albeit very infrequently and only in a well-staged ambush. [136] One of the most surprising heavy contributors are the icterids, despite their slightly smaller size and tendency to travel in large, wary flocks, 12 species are known to be hunted. [85] [86] One species pair, the meadowlarks, are most often selected as they do not flock in the same ways as many other icterids and often come to the ground, throughout their life history, rarely leaving about shrub-height. The 100.7 g (3.55 oz) western meadowlark (Sturnella neglecta), in particular, was the third most often detected bird prey species in North America. [5] [4] [85] [86] [89] Red-winged blackbirds (Agelaius phoeniceus) which are probably too small, at an average weight of 52.4 g (1.85 oz), and fast for a red-tailed hawk to ever chase on the wing (and do travel in huge flocks, especially in winter) are nonetheless also quite often found in their diet, representing up to 8% of the local diet for red-tails. It is possible that males, which are generally bold and often select lofty perches from which to display, are most regularly ambushed. [5] [161] One bird species that often flocks with red-winged blackbirds in winter is even better represented in the red-tail’s diet, the non-native 78 g (2.8 oz) European starling (Sturnus vulgaris), being the second most numerous avian prey species and seventh overall in North America. [85] [86] Although perhaps most vulnerable when caught unaware while calling atonally on a perch, a few starlings (or various blackbirds) may be caught by red-tails which test the agile, twisting murmurations of birds by flying conspicuously towards the flock, to intentionally disturb them and possibly detect lagging, injured individual birds that can be caught unlike healthy birds. However, this behavior has been implied rather than verified. [5] [119]

Over 50 passerine species from various other families beyond corvids, icterids and starlings are included in the red-tailed hawks' prey spectrum but are caught so infrequently as to generally not warrant individual mention. [85] [86] Non-passerine prey taken infrequently may include but are not limited to pigeons and doves, cuckoos, nightjars, kingfishers and parrots. [9] [89] [119] [166] [167] [168] [169] However, of some interest, is the extreme size range of birds that may be preyed upon. Red-tailed hawks in Caribbean islands seem to catch small birds more frequently due to the paucity of vertebrate prey diversity here. Birds as small as the 7.7 g (0.27 oz) elfin woods warbler (Setophaga angelae) and the 10 g (0.35 oz) bananaquit (Coereba flaveola) may turn up not infrequently as food. How red-tails can catch prey this small and nimble is unclear (perhaps mostly the even smaller nestlings or fledglings are depredated). [5] [9] [100] In California, most avian prey was stated to be between the size of a starling and a quail. [5] [119] Numerous water birds may be preyed upon including at least 22 species of shorebirds, at least 17 species of waterfowl, at least 8 species of heron and egrets and at least 8 species of rails, plus a smaller diversity of grebes, shearwaters and ibises. [5] [85] [86] [170] These may range to as small as the tiny, mysterious and "mouse-like" black rail (Laterallus jamaicensis), weighing an average of 32.7 g (1.15 oz), and snowy plover (Charadrius nivosus), weighing an average of 42.3 g (1.49 oz) (how they catch adults of this prey is not known), to some gulls, ducks and geese as heavy or heavier than a red-tailed hawk itself. [171] [172]

How large of a duck that red-tailed hawks can capture may be variable. In one instance, a red-tailed hawk failed to kill a healthy drake red-breasted merganser (Mergus serrator), with this duck estimated to weigh 1,100 g (2.4 lb), later the same red-tail was able to dispatch a malnourished red-necked grebe (Podiceps grisegena) (a species usually about as heavy as the merganser), weighing an estimated 657 g (1.448 lb). [173] However, in interior Alaska, locally red-tailed hawks have become habitual predators of adult ducks, ranging from 345 g (12.2 oz) green-winged teal (Anas carolinensis) to 1,141 g (2.515 lb) mallard (Anas platyrhynchos). [77] Even larger, occasionally adult Ross's goose (Chen rossii), weighing on average 1,636 g (3.607 lb), have been killed as well. [174] Also, a non-native Egyptian goose (Alopochen aegyptiaca), in which adults average 1,762 g (3.885 lb), was killed by a red-tail in Texas. [175] There are several known instances of predation on adult greater sage grouse (Centrocercus urophasianus), although mainly females are reported taken, these averaging 1,200 to 1,745 g (2.646 to 3.847 lb) depending on region. Some adult male sage grouse may have been attacked but, as these average from 2,100 to 3,190 g (4.63 to 7.03 lb), this needs verification. [154] Even larger, in at least once case a grown hatch-year bird was caught of the rare, non-native Himalayan snowcock (Tetraogallus himalayensis), this species averaging 2,428 g (5.353 lb) in adults. [176] Red-tailed hawks are a threat to the poults typically of the wild turkey (Meleagris gallopavo). However, in one instance, an immature red-tail was observed trying to attack an adult female turkey, which would weigh about 4,260 g (9.39 lb) (on average). However this red-tail was unable to overpower the turkey hen. [177] Additionally, young domestic turkeys, weighing up to at least 1,500 g (3.3 lb) or more, have been killed by red-tailed hawks. [178] Other than wild turkeys, other larger birds occasionally lose young to red-tails such as trumpeter swans (Cygnus buccinator), sandhill cranes (Grus canadensis) and great blue herons (Ardea herodias). [179] [180]

Reptiles Edit

Early reports claimed relatively little predation of reptiles by red-tailed hawks but these were regionally biased towards the east coast and the upper Midwest of the United States. [181] However, locally the predation on reptiles can be regionally quite heavy and they may become the primary prey where large, stable numbers of rodents and leporids are not to be found reliably. Nearly 80 species of reptilian prey have been recorded in the diet at this point. [5] [85] [86] Most predation is on snakes, with more than 40 species known in the prey spectrum. The most often found reptilian species in the diet (and sixth overall in 27 North American dietary studies) was the gopher snake (Pituophis catenifer). Red-tails are efficient predators of these large snakes, which average about 532 g (1.173 lb) in adults, although they also take many small and young gopher snakes. [89] [122] [182] [183] [184] Along the Columbia River in Washington, large colubrid snakes were found to be the primary prey, with the eastern racer (Coluber constrictor), which averages about 556 g (1.226 lb) in mature adults, the most often recorded at 21.3% of 150 prey items, followed by the gopher snake at 18%. This riverine region lacks ground squirrels and has low numbers of leporids. 43.2% of the overall diet here was made up of reptiles, while mammals, made up 40.6%. [182] [185] In the Snake River NCA, the gopher snake was the second most regularly recorded (16.2% of 382 items) prey species over the course of the years, and did not appear to be subject to the extreme population fluctuations of mammalian prey here. [89] Good numbers of smaller colubrids can be taken as well, especially garter snakes. [85] [91] [109] Red-tailed hawks may engage in avoidance behavior to some extent with regard to venomous snakes. For example, on the San Joaquin Experimental Range in California, they were recorded taking 225 gopher snakes against 83 western rattlesnakes (Crotalus oreganus). Based on surveys, however, the rattlesnakes were five times more abundant on the range than the gopher snakes. [5] [119] Nonetheless, at least 15 venomous snakes have been recorded in the red-tailed hawk’s diet. [85] [86] The smallest known snake known to be hunted by red-tailed hawks is the 6 g (0.21 oz) redbelly snake (Storeria occipitomaculata). [186] Red-tailed hawks have been seen flying off with snake prey that may exceed 153 cm (5 ft 0 in) in length in some cases. [9] One red-tail was photographed killing a "fairly large" eastern diamondback rattlesnake (Crotalus adamanteus), this being North America’s heaviest snake and the heaviest venomous snake in the Americas at a large mature size of about 2,300 g (5.1 lb). [16] [187] For the eastern indigo snakes (Drymarchon couperi), North America’s longest native snake, usually young and small ones are at risk. [188]

In North America, fewer lizards are typically recorded in the foods of red-tailed hawk than are snakes, probably because snakes are considerably better adapted to cooler, seasonal weather, with an extensive diversity of lizards found only in the southernmost reaches of the contiguous United States. A fair number of lizards were recorded in the diet in southern California and red-tails can be counted among the primary predatory threats to largish lizards in the United States such as the 245 g (8.6 oz) common chuckawalla (Sauromalus ater). [86] [119] [189] [190] However, the red-tailed hawks ranging into the neotropics regularly take numerous species of lizards. This is especially true of hawks living on islands which are not naturally colonized by small mammals. Insular red-tails commonly pluck up mostly tiny anoles, that may average only 1.75 to 43.5 g (0.062 to 1.534 oz) in adult mass, depending on species. [9] [100] [191] Not all tropical lizards taken by red-tailed hawks are so dainty and some are easily as large as most birds and reptiles taken elsewhere such as adults of the 1,800 g (4.0 lb) San Esteban chuckwalla (Sauromalus varius) and even those as large as 2,800 g (6.2 lb) Cape spinytail iguanas (Ctenosaura hemilopha) and 4,000 g (8.8 lb) green iguanas (Iguana iguana) (though it is not clearly noted whether they can take healthy adults iguanas or not). [192] [193] [194] Beyond snakes and lizards, there are a few cases of red-tailed hawks preying on baby or juvenile turtles, i.e. the gopher tortoise (Gopherus polyphemus), the desert tortoise (Gopherus agassizii) and the common snapping turtle (Chelydra serpentina). [143] [195]

Other prey Edit

Records of predation on amphibians is fairly infrequent. It is thought that such prey may be slightly underrepresented, as they are often consumed whole and may not leave a trace in pellets. Their fine bones may dissolve upon consumption. [5] [85] [181] So far as is known, North American red-tailed hawks have preyed upon 9 species of amphibian, four of which are toads. Known amphibian prey has ranged to as small as the 0.75 g (0.026 oz) red-backed salamander (Plethodon cinereus), the smallest known vertebrate prey for red-tailed hawks, to the 430 g (15 oz) American bullfrog (Lithobates catesbeianus). [126] [143] [196] Invertebrates, mostly represented by insects like beetles and crickets, are better represented in the stomach contents of red-tailed hawks than their pellets or prey remains. [5] [181] It is possible some invertebrate prey is ingested incidentally, as in other various birds of prey, they can in some cases be actually from the stomachs of birds eaten by the raptor. [2] [5] However, some red-tails, especially immatures early in their hunting efforts, often do spend much of the day on the ground grabbing terrestrial insects and spiders. [5] [85] [181] [197] [198] The red-tailed hawks of Puerto Rico frequently consume Puerto Rican freshwater crabs (Epilobocera sinuatifrons), which average 9.4 g (0.33 oz). [9] [100] [199] Other island populations, such as those on Socorro island, also feed often on terrestrial crabs, here often blunting their claws while catching them. [27] Fish are the rarest class of prey based on dietary studies. Among the rare instances of them capturing fish have included captures of wild channel catfish (Ictalurus punctatus), non-native common carp (Cyprinus carpio) and ornamental koi (Cyprinus rubrofuscus) as well some hawks that were seen scavenging on dead chum salmon (Oncorhynchus keta). [86] [200] [201]

Interspecies predatory relationships Edit

As easily one of the most abundant of all American raptorial birds, red-tailed hawks have been recorded as interacting with every other diurnal bird of prey. Due to the extreme dietary plasticity of red-tails, the food habits of other birds of prey regularly overlap considerably with red-tails. Furthermore, due to its ability to nest in varied habitats, home ranges also frequently abut those of other raptor species. [5] [9] The most obvious similar species in their range are other Buteo hawks, especially larger species with a similar ecological niche. Two of the larger, more widespread other Buteos are the Swainson's hawk and the ferruginous hawks and, as with many other birds of prey, red-tailed hawks occur in almost the entirety of these birds' breeding ranges. [9] [202] These species have broadly similar breeding season diets, especially the ferruginous and red-tailed hawks. In some areas, such as Snake River NCA the diets of the two species consist of more than 90% of the same species and body mass of prey taken was similar. [89] [91] Therefore, all three large Buteo hawks defend their territories from each other with almost the same degree of dedication that they defend from others of their own species. In some cases, territorial clashes of Swainson's hawks and red-tailed hawks can last up to 12 hours, however, the birds involved are usually careful to avoid physical contact. [5] [203] Due to the similarities of the foods and their aggressive dispositions towards one another, these Buteos need some degree of partitioning in order to persist alongside one another and this usually is given by habitat preferences. The ferruginous hawk prefers open, practically treeless prairie while of these, the red-tailed hawks prefers the most wooded areas with large trees, while the Swainson's hawk prefer roughly intermediate areas. [91] [203] [8] Where the habitat is more open, such as in Cassia County, Idaho, the Swainson's and ferruginous hawks have the advantage in numbers and red-tails are scarce. [204] However, habitat alterations by humans, such as fire suppression and recovering pasture, usually favor the red-tailed hawk and are to the detriment of the other two species. [202] [205] [64] These practices have caused range expansions of many other species of birds but declines in many others. [206] [207] [208] Of these three Buteo species, the Swainson's hawk is most dissimilar, being a long-distance migrant which travels to South America each winter and, for much of the year, prefers to prey on insects (except for during breeding, when more nutritious food such as ground squirrels are mainly fed to the young). It also breeds notably later than the other two species. [209] Surprisingly, although it's slightly smaller in body mass and has notably smaller (and presumably weaker) feet than ferruginous and red-tailed hawks, the Swainson's is actually usually (but not invariably) dominant in territorial conflicts over the other two. Part of this advantage is that the Swainson's hawk is apparently a superior flier both in long and short-distance flights, with its more pointed wing shape and lower wing loading allowing it more agile, sustained and speedier flight that the bulkier hawks cannot match. [210] Therefore, in north-central Oregon, Swainson's hawks were shown to be more productive, in prairie located trees, and partially displaced prior-breeding red-tails several times, although overall breeding success rates were not perceptibly decreased in the latter hawk. [203] [211] In the Chihuahuan Desert of Mexico, Swainson's hawks usually nested in lowlands and red-tails nested in highlands but interspecies conflicts nevertheless were apparently quite frequent. Usually, the habitat preferences of red-tailed hawks and ferruginous hawks are discrepant enough to keep serious territorial conflicts to a minimum. [89] [203] However, red-tailed hawks and ferruginous hawks occasionally engaged in kleptoparasitism towards one another, usually during winter. Red-tails may be somewhat dominant based on prior reports in food conflicts but the ferruginous hawk may also win these. [4] Where they overlap, the hawk species may adjust their daily routine to minimize contact, which tends to be costly of time and energy and may cause the hawks to abandon their nests for long stretches of time, which in turn leaves their young vulnerable to predation. [5] When habitats change rapidly, often due to human interference, and the species nest more closely than natural partitioning would allow, in all three nesting success can decline significantly. [8]

Beyond the Swainson's and ferruginous hawks, six other Buteos co-occur with red-tailed hawks in different parts of North America. Many of these are substantially smaller than red-tails and most serious territorial conflicts with them are naturally mitigated by nesting in deeper wooded areas. [65] [202] One other larger species, the rough-legged buzzard, mostly nests far north of the breeding range of red-tailed hawks. However, in Alaska they sometimes nest in the same areas. The rough-legged buzzards are both cliff and tree nesters and areas used by the two species are not necessarily mutually exclusive but each seems to avoid the other, in part by differing breeding schedules. [212] Wintering rough-legged buzzards may regularly come into conflict over food with red-tailed hawks and seem to be subordinate to the red-tails, with several records of them being chased off both kills and carrion by the red-tailed hawks. During winter their hunting habits may keep them somewhat separate, the rough-legged being a much more aerial hunter, but rough-legged buzzards usually withdrew if a red-tailed hawk flew towards them. There is at least one case, however, of a rough-legged buzzard being the victor of a conflict over a kill with a red-tailed hawk. [77] [147] Red-tailed hawks are conspicuously more aggressive and tend to be dominant over slenderer, medium-sized Buteos such as red-shouldered hawks and zone-tailed hawks (Buteo albonotatus). [27] In Massachusetts, red-shoulder hawks used mixed forests and hardwoods as nesting habitat while red-tails most often used in pitch pine and stunted oaks on Cape Cod. Nesting range overlap here most often occurred on white pine forests. As habitat has opened over time, red-tailed hawks frequently took over former red-shouldered hawk territories, even using their nests in two cases. [5] [65] In north-central Florida, it was found during winter that red-shouldered and red-tailed hawk habitat usage blurred and, because the local habitat favors red-shouldered hawks, they easily outnumbered the number of red-tailed hawks in the area. Therefore, again with sufficient habitat partitioning, the two species can live near one another without negatively effecting one another. [213] In the American southwest and Texas, two relatively large buteonine hawks also live alongside red-tailed hawks, the Harris's hawk (Parabuteo unicinctus) and the white-tailed hawk (Geranoaetus albicaudatus). Usually, habitat preferences kept conflicts to a minimum, with the red-tailed hawk favoring taller, more isolated saguaro cactus for nesting, whereas the other species outnumbered red-tails in areas that were denser and more shrubby. [214] [215] The Harris's hawk was determined to be a superior aerial hunter over red-tailed hawks, and could take down flying birds more routinely. [214]

Hawks and kites from outside the buteonine lineage are usually substantially smaller or at least different enough in diet and habitat to largely avoid heavy conflict with red-tailed hawks. On occasion, northern harriers (Circus hudsonius) which have much lower wing loading, will mob red-tailed hawks out of their home ranges but in winter the red-tails seem to be dominant over them in conflicts over food. [147] [216] Among Accipiter hawks, the most similar to the red-tailed hawk in diet and size is the northern goshawk. In some areas, the prey species of these can be very similar and North American populations of goshawks take many more squirrels and leporids than their Eurasian counterparts do. [128] [217] It was found that the feet and striking force of hunting goshawks was more powerful than that of the red-tailed hawk, despite the red-tails being up to 10% heavier in some parts of North America. [94] Therefore, wild goshawks can dispatch larger prey both on average and at maximum prey size, with some victims of female goshawks such as adult hares and galliforms such as turkey and capercaillie weighing up to or exceeding roughly 4,000 g (8.8 lb). [218] [219] [220] In a comparative study in the Kaibab Plateau of Arizona, however, it was found that red-tailed hawks had several population advantages. Red-tails were more flexible in diet, although there was a very broad overlap in prey species selected, and nesting habitat than the goshawks were. [136] As red-tailed hawks in conflict with other more closely related Buteo hawks rarely (if ever) result in mortality on either side, goshawks and red-tailed hawks do seem to readily kill one another. Adults of both species have been shown to be able to kill adults of the other. [125] [221] [222] [223]

The great horned owl occupies a similar ecological niche nocturnally to the red-tailed hawk. [88] There have been many studies that have contrasted the ecology of these two powerful raptors. [39] [84] [129] The great horned owl averages heavier and larger footed, with northern populations averaging up to 26% heavier in the owl than the hawk. [39] However, due in part to the red-tail’s more extensive access to sizable prey such as ground squirrels, several contrasting dietary studies found that the estimated mean prey size of the red-tailed hawk, at 175 g (6.2 oz), was considerably higher than that of the great horned owl, at 76 g (2.7 oz). [88] Also, the diet of red-tailed hawk seems to be more flexible by prey type, as only just over 65% of their diet is made of mammals, whereas great horned owls were more restricted feeders on mammals, selecting them 87.6% of the time. [85] [86] [224] However, the overall prey spectrum of great horned owls includes more species of mammals and birds (but far less reptiles) and the great horned owl can attack prey of a wider size range, including much larger prey items than any taken by red-tailed hawks. Mean prey weights in different areas for great horned owls can vary from 22.5 to 610.4 g (0.79 to 21.53 oz), so is far more variable than that of red-tailed hawks (at 43.4 to 361.4 g (1.53 to 12.75 oz)) and can be much larger (by about 45%) than the largest estimated size known for the red-tailed hawk's mean prey weight but conversely the owl can also subsist on prey communities averaging much smaller in body size than can support the hawk. [225] [226] Some prey killed by great horned owls was estimated to weigh up to 6,800 g (15.0 lb). [85] [224] [227] Great horned owls and red-tailed hawks compete not only for food but more seriously over nesting areas and home ranges. Great horned owls are incapable of constructing nests and readily expropriate existing red-tail nests. The habitat preferences of the two species are quite similar and the owl frequently uses old red-tail nests, but they do seem to prefer more enclosed nest locations where available over the generally open situation around red-tailed hawk nests. Sometimes in warmer areas, the owls may nest sufficiently early to have fledged young by the time red-tails start to lay. However, when there is a temporal overlap in reproductive cycles, the owl sometimes takes over an occupied red-tail nest, causing desertion. Red-tailed hawks have an advantage in staple prey flexibility as aforementioned, while great horned owl populations can be stressed when preferred prey is scarce, especially when they rely on leporids such as hares and jackrabbits. [5] [88] [128] [112] For example, in Alberta, when snowshoe hares were at their population peak, red-tailed hawks did not increase in population despite taking many, with only a slight increase in mean clutch size, whereas the owls fluctuated in much more dramatic ways in accordance with snowshoe hare numbers. The red-tails migratory behavior was considered as the likely cause of this lack of effect, whereas great horned owls remained through the winter and was subject to winter-stress and greater risk of starvation. [228] As a nester, great horned owl has the advantage in terms of flexibility, being somewhat spread more evenly across different habitats whereas in undisturbed areas, red-tailed hawks seem to nest more so in clusters where habitat is favorable. [5] [84] [129] [228] Predatory relationships between red-tailed hawks and great horned owls are quite one-sided, with the great horned owl likely the overall major predator of red-tails. On the other hand, red-tailed hawks are rarely (if ever) a threat to the great horned owl. Occasionally a red-tailed hawk can strike down an owl during the day but only in a few singular cases has this killed an owl. [229] [230] Most predation by the owls on the hawks is directed at nestlings at the point where the red-tails' nestlings are old enough that the parents no longer roost around the nest at night. Up to at least 36% of red-tailed hawk nestlings in a population may be lost to great horned owls. [5] [125] Adult and immature red-tailed hawks are also occasionally preyed upon at night by great horned owls in any season. In one case, a great horned owl seemed to have ambushed, killed and fed upon a full-grown migrating red-tail even in broad daylight. [5] [65] Occasionally, both red-tails and great horned owls will engage each other during the day and, even though the red-tailed hawk has the advantage at this time of day, either may succeed in driving away the other. [4] [65] [228] Despite their contentious relations, the two species may nest quite close to one another. For example, in Saskatchewan, the smallest distance between nests was only 32 to 65 m (105 ft 0 in to 213 ft 3 in). In these close proximity areas all owl nests succeeded while only two red-tail nests were successful. [231] In Waterloo, Wisconsin, the two species were largely segregated by nesting times, as returning red-tailed hawks in April–June were usually able to successfully avoid nesting in groves holding great horned owls, which can begin nesting activities as early as February. [232] In Delaware County, Ohio and in central New York state, divergence of hunting and nesting times usually allowed both species to succeed in nesting. In all three areas, any time the red-tails tried to nest closer to great horned owls, their breeding success rates lowered considerably. It is presumable that sparser habitat and prey resources increased the closeness of nesting habits of the two species, to the detriment of the red-tails. Due to nesting proximity to great horned owls, mature red-tails may have losses ranging from 10 to 26%. [125] [129] [231] [233]

Red-tailed hawks may face competition from a very broad range of predatory animals, including birds outside of typically active predatory families, carnivoran mammals and some reptiles such as snakes. Mostly these diverse kinds of predators are segregated by their hunting methods, primary times of activity and habitat preferences. In California, both the red-tails and western diamondback rattlesnakes (Crotalus atrox) live mainly on California ground squirrel, but the rattlesnake generally attacks the squirrels in and around their burrows, whereas the hawks must wait until they leave the burrows to capture them. [234] Hawks have been observed following American badgers (Taxidea taxus) to capture prey they flush and the two are considered potential competitors, especially in sparse sub-desert areas where the rodent foods they both favor are scarce. [235] Competition over carcasses may occur with American crows, and several crows, usually about six or more, working together can displace a hawk. [236] Another avian scavenger, the turkey vulture (Cathartes aura), is dominated by red-tails and may be followed by red-tails in order to supplant a carcass found by the vulture with their keen sense of smell. [237] In some cases, red-tailed hawks may be considered lessened as food competitors by their lack of specialization. For instance, no serious competition probably occurs between them and Canada lynx (Lynx canadensis) despite both living on snowshoe hares. [238]

Distinguishing territorial exclusionary behavior and anti-predator behavior is difficult in raptorial birds. However, as opposed to other medium to largish hawks which chase off red-tails most likely as competition, in much smaller raptors such as kestrels and smaller Accipiter hawks, their aggressive reaction to red-tailed hawks is almost certainly an anti-predator behavior. Although less prolific than goshawks, some eagles and, especially, great horned owls, red-tailed hawks can and do prey upon smaller birds of prey. The following species of accipitrid have been known to fall prey to red-tailed hawks, potentially including nestlings, fledglings, immatures and/or adults: swallow-tailed kite (Elanoides forficatus), [239] Mississippi kite (Ictinia mississippiensis), [240] white-tailed kite (Elanus leucurus), [241] northern harrier (Circus hudsonius), [86] sharp-shinned hawk (Accipiter striatus), [242] Cooper's hawk (Accipiter cooperii), [243] goshawks, [223] gray hawk (Buteo plagiatus), [244] red-shouldered hawk [245] and broad-winged hawk (Buteo platypterus). [246] These species range from the 135.7 g (4.79 oz) sharp-shinned hawk, the smallest North American accipitrid, to the goshawk, which at 956 g (2.108 lb) is nearly red-tailed hawk sized. [223] Additionally, there are records of red-tailed hawks hunting 9 species of owl, ranging in size from the 104.2 g (3.68 oz) northern saw-whet owl (Aegolius acadius) to juveniles of the 1,079 g (2.379 lb) great gray owl (Strix nebulosa) and seemingly adults of the 717 g (1.581 lb) barred owl (Strix varia). [85] [86] Red-tails will also hunt falcons including adult American kestrels (Falco sparverius) and merlins (Falco columbarius) and presumed nestlings of the peregrine falcon (Falco peregrinus). [86] [247] [248] When hunting other raptorial birds, red-tailed hawks seem to ambush them from a perch, diving suddenly and unexpectedly upon spotting the quarry and tend to have the greatest success when the raptorial prey is distracted, such as those migrating on windy days, feeding on their own prey and tending to their nest. [5] [223] [247]

In turn, red-tailed hawks may engage in behavior that straddles territorial exclusion and anti-predator behavior to the two much larger raptors in North America which actively hunt, the eagles. Red-tails are most commonly seen flying towards and aggressively displacing both flying bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos), but may also, to the contrary, unobtrusively duck down out of flight to an inconspicuous perch when an eagle is spotted. The behavioral variation is probably related to the activity of hawks, which may feel the need to protect their nests and food resources while actively breeding but are not usually willing to risk their lives in attacking an eagle while migrating or wintering. At times mobbing behavior of smaller raptors may cause both eagles to turn over and present their large talons to their attacker, which can be dangerous for the smaller hawk. [5] [119] [203] [249] Besides the great horned owl, the two eagle species are the only known animals known to regularly threaten red-tailed hawks of any age. In particular, the golden eagle is probably the greatest daytime threat to fledged immature and adult red-tails, as these have turned up in many dietary studies of the powerful eagle. [85] [250] Less efficient as a predator of red-tails, bald eagles nonetheless have been recording killing adults in some cases or, more often, depredating red-tailed hawk nests. On occasion, this may result in the bald eagle bringing the nestling red-tails to their own nest and, for some reason, not killing them. In some cases, the bald eagles inadvertently actually raise the nestling red-tails themselves and the baby red-tailed hawks may successfully fledge. [251] In one case, a red-tailed hawk was observed to kill a bald eagle chick, whether this was predatory or competitive, it quickly abandoned the dead nestling after the eagle’s parents returned. [252] On several tropical islands, which are often shared only with other hawks, owls and falcons of only medium or small size and typically lack larger raptors or carnivorans, the red-tailed hawk may be the largest native predator and will, in these cases, be considered the apex predator. [253] [254] Other than large birds of prey, extensive records of predation on red-tailed hawks is surprisingly poor, in spite of several populations recording nestlings and eggs disappearing through presumed acts of natural predation. The most likely major predator of eggs and nestlings that disappear is the raccoon which, during its nocturnal foraging, is a notorious enemy of nearly any kind of birds nest. [5] [4] [255] It is also known that unidentified large snakes, probably consisting of the same species that the red-tails so readily predate during broad daylight, will prey upon nestling red-tails. [256] In California, common ravens were recorded preying on the downy young of red-tailed hawks. [257] Other corvids, including blue jays (Cyanocitta cristata), California scrub jays (Aphelocoma californica) and crows, are known to feed on eggs and small nestlings either when nest attendance is atypically low by the hawks or when they can successful harass the parent hawks via mobbing so severely that they temporarily leave the nest. [4] [27] [258] Blackflies (Simulium canonicolum) have been recorded as killing several red-tail chicks through blood loss. [259] There are also several cases of possible prey turning the tables on red-tailed hawks and either maiming or killing them. This is especially true of snakes, with some prey species of Pituophis, Pantherophis and Coluber known to overpower and nearly kill, often the hawk survives only if by human intervention. Not infrequently prey such as coral snakes and rattlesnakes may succeed in killing red-tailed hawks with their venom, even if they themselves are also killed and partially consumed. [119] [184] [260] [261] Peregrine falcons are also known to kill red-tailed hawks that have come too close to their nests by stooping upon them. [5]

Courtship and pre-laying behaviors Edit

Pairs either court for the first time or engage in courtship rituals to strengthen pre-existing pair bonds before going into the breeding. The breeding season usually begins in late February through March, but can commence as early as late December in Arizona and late January in Wisconsin or to the opposite extreme as late as mid-April as in Alberta. [9] [84] [125] [214] In this pre-nesting period, high-circling with much calling will occur. One or both members of a pair may be involved. The courtship display often involves dangling legs, at times the pair will touching each other's wings and male's feet may touch female's back, she may occasional roll over and present talons, food passes are rarely reported. [2] [9] [77] High soaring occurs aseasonally. Circling above territory tends to be done noisily and conspicuously, helping insure against possible takeovers. Spring circling of a pair can be a prelude to copulation. [27] A typical sky-dance involves the male hawk climbing high in flight with deep, exaggerated beats and then diving precipitously on half-closed wings at great speed, checking, and shooting back up, or often plunging less steeply and repeating process in a full rollercoaster across the sky. Sky-dances are done on periphery of the pair’s territory and it appears to designate the territory limits, occasionally one male’s sky-dance may also trigger a sky-dance by a neighboring male, who may even run a parallel course in the sky. Sky-dances no longer occur after late incubation. [2] [5] [65] Boundary flight displays may be engaged in by all four birds of 2 adjacent pairs. [27] Cartwheeling with interlocking talons is also seen occasionally in spring, almost always a territorial male expelling an intruding one, the latter often being a second or third year male that is newly mature. A perched display, with fluffed-out breast feathers may too occur at this time. Even males that are in spring migration have been recorded engaging in a separate display: circling at slow speed before partially closing wings, dropping legs with talons spread and tilting from side-to-side. A female hawk is usually around when migrating male does this but she does not engage in this display herself. [2] [5] The area of occupancy of breeding territories by pairs is variable based on regional habitat composition. The highest recorded density of pairs was in California where each pair occurred on 1.3 km 2 (0.50 sq mi), which was actually just ahead of Puerto Rico where pair occupancy averaged 1.56 km 2 (0.60 sq mi) in peak habitat. The largest known average territory sizes were surprisingly in Ohio, where the average area of occupancy by pairs was recorded as 50 km 2 (19 sq mi). [9] [100] [119] In Wisconsin mean ranges for males range from 1.17 to 3.9 km 2 (0.45 to 1.51 sq mi) in males and from 0.85 to 1.67 km 2 (0.33 to 0.64 sq mi) in females, respectively in summer and winter. Here and elsewhere, both members of the pair stay quite close together throughout winter if they are sedentary. On the other hand, migrant populations tend to separate while migrating and return to the same territory to find its prior mate, sometimes before they reach their home range. [9] [100] [232] In Alaska, returning migrant pairs were able to displace lone red-tailed hawks that had stayed on residence, especially lone males but sometimes even lone females. [77] In general, the red-tailed hawk will only take a new mate when its original mate dies. [262] Although pairs often mate for life, replacement of mates can often be quite fast for this common bird species. In one case in Baja California, when a female was shot on 16 May, the male of that pair was seen to have selected a new mate the following day. [5] [263] In copulation, the female, when perched, tilts forward, allowing the male to land with his feet lodged on her horizontal back. The female twists and moves her tail feathers to one side, while the mounted male twists his cloacal opening around the female's cloaca. Copulation lasts 5 to 10 seconds and during pre-nesting courtship in late winter or early spring can occur numerous times each day. [264]

Nests Edit

The pair constructs a stick nest most often in a large tree 4 to 21 m (13 to 69 ft) off the ground. They may too nest on virtually any man-made structures with some variety of ample ledges or surface space and good views of the surrounding environment (i.e. powerline poles, radio transmission towers, skyscraper buildings). [9] [5] [62] [265] [266] [267] Much variation is recorded in nest usage behavior, many red-tails build new nests every year despite prior nests sometimes being in good standing and unoccupied, some may reuse a nest in subsequent years or may leave a nest for a year and then come back to it the following year. [9] [5] A red-tailed hawk nest is typically located in a gradient zone between woods with tall, mature trees, if available, and openings whether this is composed of shrubland, grassland or agricultural areas. [268] Nest sites vary greatly in topography and vegetative composition. [269] While tree nests are largely preferred, occasionally the species nests on cliff ledges may be utilized even where other nest sites are presumably available. Cliff nests may be located at 35 m (115 ft) or higher above the nearest flat ground. [5] [270] [271] At times, unlike great horned owls, red-tailed hawks have been recorded nesting in surprisingly unbroken forests. [272] In North Dakota, nest sites tend to be concentrated along wooded river drainages. [273] Compared to Swainson's hawks and ferruginous hawks, red-tailed hawk nests are usually in taller trees and are closer to waterways. [8] [274] In Puerto Rico, nests are most often found in transitional zone between dry lowlands and mountainous cloud forests, with trees typically taller than their neighbors to allow views of more than half of their home ranges. More than 21 tree species were recorded used in Puerto Rico. [100] Tree species is seemingly unimportant to red-tailed hawks. [275] In some parts of Arizona, saguaro cactus were used exclusively as nesting sites. [214] Alternately, old nests of other Buteo hawks, corvids, golden eagles and even leaf nests of tree squirrels have also been used by red-tailed hawks. [2] Both members of the pair will build the nests but the female spends more time forming the bowl, with the greatest activity often in the morning and nest building completed in a week or less. [84] [119] The nest is generally 71 to 97 cm (28 to 38 in) in diameter, with a mean of roughly 76 cm (30 in), and can be up to 96 cm (38 in) tall after several years use. The inner bowl averages about 37 cm (15 in) wide and 13 cm (5.1 in) deep. [9] [65] [232] The nest is constructed of twigs, and lined with bark, pine needles, corn cobs, husks, stalks, aspen catkins, or other plant lining matter. Lining the nest may be for warning other red-tails of the active use of a nest. [9] [84] In moderate to northern climes, red-tailed hawks tend to face to the south or west, presumably to make them less vulnerable to strong northeasterly storm winds. [276]

Eggs Edit

In most of the interior contiguous United States the first egg is laid between mid-March and early April, ranging from 3 to 5 weeks after the nest is constructed, with the clutch completed 2 to 5 days after the initial egg is laid. [9] [277] The average date of the laying the first egg can be variable: peaking mid-January in Puerto Rico, averaging 9 March in Arizona, 26 March in the Front Range Urban Corridor and 1 May in Alberta. [9] [100] [125] [214] The mean initiation of clutches may bump weeks later if 10 cm (3.9 in) or more of snow is still on the ground in Wisconsin during March. [84] A clutch of one to three eggs is laid in March or April, depending upon latitude, with four eggs being uncommon and five and perhaps even six increasingly rare. [65] Clutch size depends almost exclusively on the availability of prey for the adults. At the species level, body size also determines clutch size. For example, while the total clutch weighs up to 18% of the females weight and the clutch size averages 2 to 3, a larger raptor like the golden eagle lays a smaller clutch, usually not more than two, that weighs less than 10% in total of the female’s body mass, whereas a smaller raptor like the kestrel lays a larger clutch averaging five that weighs 50% of the females weight. [4] Average clutch size vary from 1.96 in Alaska when prey populations were low up to 2.96 in Washington. [77] [278] Eggs are laid approximately every other day. Average egg sizes in height and width (each with a sample size of 20) are in the following subspecies- B. j. borealis: 59.53 mm × 47.49 mm (2.344 in × 1.870 in) B. j. calurus: 60.04 mm × 47.1 mm (2.364 in × 1.854 in) B. j. fuertesi: 59.42 mm × 46.99 mm (2.339 in × 1.850 in). [279] The eggs of red-tailed hawks are mostly white, sometimes with a faint buffy wash at times the eggs manifest a sparsely or heavily marked with blotches of buff, pale reddish-brown, dark brown, or purple. The markings often appear indistinctly and may combine to form a fine speckling. [280] They are incubated primarily by female, with the male substituting when the female leaves to hunt or merely stretch her wings. Rarely do the males incubate more than four hours of daylight. The male brings most food to the female while she incubates. [9] [65] [232] [257]

Hatching, development and brooding Edit

After 28 to 35 days of incubation (averaging about three days longer in the Caribbean as does fledgling as compared to North American red-tails), the eggs hatch over 2 to 4 days. [2] [281] Like most raptorial birds, the nestlings are altricial and nidicolous at hatching. [9] [119] Hatchlings average 58 g (2.0 oz) in body mass with no difference in sizes of the sexes until the young are about 29 days old for mass and 21 days or so for external linear standard measurements such as bill and talon size. [282] The female broods them while the male provides most of the food to the female and the young, which are also known as eyasses (pronounced "EYE-ess-ez"). The female feeds the eyasses after tearing the food into small pieces. The young red-tails are active by the second day when they issue soft peeping calls, bounce, and wave continuously with their wings. By day 7, the bouncing and peeping begin to wane, and young start to peck at prey in their nest. Nestlings emit high whistling notes (usually in response to adults overhead) by day 10, sit up on tarsometatarsi by day 15, become aggressive toward intruders by day 16, strike out with talons and wings by day 21, begin to stretch wings and exercise regularly by day 30. After 42 to 46 days, the eyasses begin to leave the nest and tear apart prey for themselves. [9] [119] The amount of food brought to the nest daily varies considerably, based on brood size and prey availability. In Alberta, an average of 410 to 730 g (14 to 26 oz) is brought each day for 1 to 3 nestlings while in Washington, it was estimated a minimum of 520 g (1.15 lb) per day for 1 surviving nestling and in Wisconsin, an estimated 219 g (7.7 oz) was needed for 1 nestling and 313 g (11.0 oz) for 2. [232] [228] [283] Brooding is strenuous for parent red-tails and both members of the pair usually lose some weight, especially the female. Some females may lose over 100 g (3.5 oz) between hatching and fledging. [9] During brooding the female may become aggressive to intruders, including humans. In the east, red-tailed hawk females rarely defend nests from humans but historically in California and quite often still in Alaska, some female will dive repeatedly and "savagely", sometimes snapping off large branches in her temper, occasionally stunning herself or inadvertently knocking down her own youngster if it is attempting to fledge. Apparently, the less extensive prior exposure they have to humans may make mature females more aggressive towards humans near the nest. [5] [27] [77] Although development is asynchronical in most nests, runting may sometimes be recorded and even siblicide may occur, with the parents feeding the weaker, younger chicks less so and both the siblings and parents occasionally aggressively pecking the "runts" of the nest. Ultimately, the runt in such cases does not usually survive and may be either found crushed in the nest, discarded out of the nest after starvation or consumed by the parents or the siblings. However, as a whole, such killings are fairly rare and only occur when food supplies are extremely low, often this being in sync with poor spring weather (such as overly rainy or cold conditions). [5] [233] [283] If there is too much food, such as California ground squirrels in California, the parents will discard remains after a day or two since decomposition of their prey invites infection, other diseases and blood-sucking insects to the nest that may endanger the nestlings. However, after about four weeks, the female often stops discarding leftover prey and the increased presence of flies may form somewhat of a risk to disease in the young but may also merely get the young to leave the nest sooner. [27] [119] One nest in California had two females and one male attended to the male performed his usual function but both females would brood and tend to the nest. [284] Additionally, bald eagles have been recorded to occasionally adopt red-tail fledglings into their nests. As recorded in Shoal Harbor Migratory Bird Sanctuary located near Sydney, British Columbia, on 9 June 2017, a juvenile red-tailed hawk was taken by a pair of bald eagles back to their nest, whereupon the chick, originally taken as prey, was accepted into the family by both the parents and the eagles' three fledglings. After surviving six weeks amongst the eagles, the fledgling, nicknamed "Spunky" by birdwatchers, had successfully begun learning to hunt and fly, showing that the aggressive hawk was able to survive amongst a nest of much larger adoptive siblings. [285] [286]

Fledging and immaturity Edit

Young typically leave the nest for the first time and attempt their first flights at about 42–46 days after hatching but usually they stay very near the nest for the first few days. During this period, the fledglings remain fairly sedentary, though they may chase parents and beg for food. Parents deliver food directly or, more commonly, drop it near the young. Short flights are typically undertaken for the first 3 weeks after fledgling and the young red-tails activity level often doubles. About 6 to 7 weeks after fledging, the young begin to capture their own prey, which often consists of insects and frogs that the young hawks can drop down to onto the ground with relative ease. At the point they are 15 weeks old, they may start attempts to hunt more difficult mammal and bird prey in sync with their newly developed skills for sustained flight, and most are efficient mammal predators fairly soon after their first attempts at such prey. Shortly thereafter, when the young are around 4 months of age, they become independent of their parents. In some extreme cases, juvenile red-tails may prolong their association with their parents to as long as they are half a year old, as was recorded in Wisconsin. [232] [4] [287] [288] After dispersing from the parental territory, juveniles from several nests may congregate and interact in a juvenile staging area. Although post-fledgling siblings in their parents care are fairly social, they are rarely seen together post distribution from their parents range. [9] [289] Usually, newly independent young hawks leave the breeding area and migrate, if necessary, earlier than adults do, however the opposite was true in the extreme north of Alaska, where adults were recorded to leave first. [289] [290] Immature hawks in migratory populations tend to distribute further in winter than adults from these populations do. [291] Immatures attempting to settle for the winter often are harassed from territory to territory by older red-tails, settling only in small, marginal areas. In some cases, such as near urban regions, immatures may be driven to a small pockets of urban vegetation with less tree cover and limited food resources. When a distant adult appear, immature may drop from a prominent perch to a more concealed one. [27] [84] In some cases, hungry immature red-tails have been recorded making attempts at hunting prey beyond their capacities, expending valuable energy, such as healthy adults of larger carnivorans such as coyotes (Canis latrans), foxes and badgers and healthy flying passerines. [5] There are some cases of red-tailed hawks, presumably younger than two years of age, attempting to breed, often with an adult bird of the opposite sex. Such cases have been recorded in Alberta, Arizona and Wisconsin, with about half of these attempts being successful at producing young. [125] [161] [278] [292] However, while adult plumage and technically sexual maturity is attained at two years old, many red-tails do not first successfully breed until they are around 3 years of age. [9]

Breeding success and longevity Edit

Breeding success is variable due to many factors. Estimated nesting success usually falls between 58% and 93%. [214] [233] Nesting success rates are probably drive primarily by prey populations, regional habitat composition, competition levels with other red-tailed hawks, predation rates (often due to great horned owls or perhaps raccoons) and human disturbance levels. [5] [9] [4] In Oregon specifically, nesting success varied primarily based on "dispersion and density of perches" secondarily to ground squirrel abundance and whether the nest of other pairs red-tails was directly visible from a nest. [203] [293] Repeated disturbances at the nest early in the nesting cycle may cause abandonment of eggs or nestlings in some cases, but seemingly pairs are less likely to abandon the young later in the season in cases of human disturbance. [5] 30% of nesting deaths in a study from Wisconsin were from nestlings falling to their death or the nest collapsing. [232] In Puerto Rico, habitat appeared to be the primary driver of breeding success, as in lowland pastures nesting success was 43% producing a mean number of fledglings of 1.5 whereas in cloud forest success was 34% producing a mean of 0.7 fledglings. [100] A modelling study in Puerto Rico showed that, apart from adult survival, nestling survival had the second greatest influence on population growth. [294] In Wyoming, 12 pairs on a 12 square mile tract produced an average of 1.4 young per pair. [27] In comparison, the mean number of fledglings was 0.96 in Michigan, 1.36 in Montana and was 1.4 in the Appalachians. [39] [287] [295] In Wisconsin, the number of young successfully to fledge ranged from 1.1 to 1.8 from year to year probably depending on staple prey numbers. [84] The record lifespan in wild for a red-tailed hawk is 25 years and 5 months from banding studies. In comparison, lifespans of up to 29.5 years have been recorded in captivity. [5] In the wild, other red-tailed hawks have lived for at least 25 years, for example, Pale Male was born in 1990, and in Spring 2014 is still raising eyasses. [62] However, of 5195 banded wild red-tailed hawks in one bander’s recordings, only 31 were reported to have survived to 17 years of age and only 11 survived for 20 years. [296] The average mortality rate at 1 year of age for red-tails is 54% and thereafter is around 20% from banding sources. [278] The estimated average lifespan of red-tailed hawks who attain maturity, per Palmer (1988), was claimed as only 6 to 7 years. [5] The main causes of mortality considered as electrocution on power lines, other collisions, shooting, consumption of poisoned baits set for other animals and collision with vehicles and other crafts. While most mortality of young red-tails is at least mainly due to natural causes, mortality of fledged or older red-tails is now mostly attributable to human killing, accidental or intentional, as well as flying into manmade materials. [2] [257] [297] Hawks in urban areas are threatened by the use of rat traps and poisoned bait to kill rodents. This generally consists of warfarin cookies which induce internal bleeding in rats and mice, and a hawk that ingests rodents who have consumed rat poison can itself be affected. [298] Red-tailed hawks are also vulnerable to fatal bacterial infections include peritonitis, myocarditis, granulamotous, sarcocystosis and mycobateriosis as well as some forms of viral infection, to which immature hawks especially, as they often have less access to coverage in poor weather conditions, are most vulnerable. [9] Neither this nor other Buteo hawks were found to be highly susceptible to long-term DDT egg-shell thinning due to being part, generally, of relatively short, terrestrial-based food chains. [4]

Use in falconry Edit

The red-tailed hawk is a popular bird in falconry, particularly in the United States where the sport of falconry is tightly regulated this type of hawk is widely available and is frequently assigned to apprentice falconers. [299] Red-tailed hawks are highly tameable and trainable, with a more social disposition than all other falcons or hawks other than the Harris's hawk. [300] They are also long lived and highly disease resistant, allowing a falconer to maintain a red-tailed hawk as a hunting companion for potentially up to two decades. [10] There are fewer than 5,000 falconers in the United States, so despite their popularity any effect on the red-tailed hawk population, estimated to be about one million in the United States, is negligible. [301]

Not being as swift as falcons or accipiters, red-tailed hawks are usually used to hunt small game such as rabbits and squirrels, as well as larger quarry such as Hares. However, some individuals may learn to ambush game birds on the ground before they are able to take off and accelerate to full speed, or as they have fly into cover after a chase. Some have even learned to use a falcon-like diving stoop to capture challenging game birds such as pheasants in open country.

In the course of a typical hunt, a falconer using a red-tailed hawk most commonly releases the hawk and allows it to perch in a tree or other high vantage point. The falconer, who may be aided by a dog, then attempts to flush prey by stirring up ground cover. A well-trained red-tailed hawk will follow the falconer and dog, realizing that their activities produce opportunities to catch game. Once a raptor catches game, it does not bring it back to the falconer. Instead, the falconer must locate the bird and its captured prey, "make in" (carefully approach) and trade the bird off its kill in exchange for a piece of offered meat. [10] [302]

A trained red-tailed hawk working with a volunteer from the Ojai Raptor Center

A falconer's red-tailed hawk comes in for a landing

Feathers and Native American use Edit

The feathers and other parts of the red-tailed hawk are considered sacred to many American indigenous people and, like the feathers of the bald eagle and golden eagle, are sometimes used in religious ceremonies and found adorning the regalia of many Native Americans in the United States these parts, most especially their distinctive tail feathers, are a popular item in the Native American community. [303] As with the other two species, the feathers and parts of the red-tailed hawk are regulated by the eagle feather law, [304] which governs the possession of feathers and parts of migratory birds. [305]


The taxonomy of the wide-ranging changeable hawk-eagle is complex and confusing, with few authorities agreeing on whether the species in fact houses a species complex. [9] Gamauf et al. (2005) analyzed mtDNA cytochrome b and control region sequence data of a considerable number of specimens of the crested hawk-eagle and some relatives. Despite the large sample, even the most conspicuous dichotomy - that between the crested and crestless groups - was not as well resolved as it might have been expected to be. [9] At least one widely accepted genetic study has resulted in a recent revision to the recognition of a new species, as the Flores hawk-eagle has traditionally been treated as a subspecies of the changeable hawk-eagle, but it is now often treated as a separate species, N. floris. [10] The Flores and changeable hawk-eagles are regarded as sister species. [11] The three small-island taxa (N. c. andamanensis, N. c. vanheurni, and N. floris) as a whole each appear as monophyletic lineages. Their placement is even more unresolved, with N. floris being apparently a very ancient lineage. The other two seem quite certainly to derive from N. c. limnaeetus. The latter taxon has a confusing phylogeny. Different lineages exist that are apparently not stable in space and time, are best described as polytomy, from which the similar island taxa derive. [9] [11] Obviously, N. c. limnaeetus does not represent a monophyletic lineage. Neither the biological nor the phylogenetic species concepts, nor phylogenetic systematics can be applied to satisfaction. The crested group apparently is close to becoming a distinct species. The island taxa derived from N. c. limnaeetus appear to have undergone founder effects, which has restricted their genetic diversity. In the continental population, genetic diversity is considerable, and the evolutionary pattern of the two studied genes did not agree, and neither did the origin of specimens show clear structures. N. c. limnaeetus thus is best considered a metapopulation. [9]

Gamauf et al. (2005) therefore suggest the island taxa which are obviously at higher risk of extinction are, for conservation considered evolutionary significant units regardless of their systematic status. This case also demonstrates that a too-rigid interpretation of cladistics and the desire for monophyletic taxa, as well as universal application of single-species concept to all birds will undermine correct understanding of evolutionary relationships. It would even not be inconceivable to find mainland lineages to group closely with the western island taxa, if little genetic drift had occurred in the initial population. nonetheless, the divergence of this species' lineages seems to have taken place too recently to award them species status, as compared to the level of genetic divergence at which clades are usually considered distinct species. [9] N. c. limnaeetus appears for all that can be said with reasonable certainty basal pool of lineages in the crestless group that, despite not being monophyletic, should be considered a valid taxon as long as gene flow is possible through its range. In addition, as ancient DNA from museum specimens was used extensively, the possibility of ghost lineages must be considered. If it is assumed that all or most of the ancient lineages still exist today, considerable recombination must have taken place as the two genes' phylogenies do not agree much, indicating a healthy level of gene flow. Whether this still holds true today remains to be determined. [9]

Two distinct groups exist in the changeable hawk-eagle one with crests and one without or with hardly visible crests. Dark morphs exist for some populations. [12]

Subspecies Edit

  • N. c. cirrhatus: The nominate subspecies is found in the peninsular India, from the Gangetic plain southwards throughout the remainder of the country. It is monomorphic in colour with no dark morph. The nominate subspecies is relatively pale above compared to other races, with a slightly more rufous hue to the head. It tends to be less extensively streaked below down to the lower breast below compared to other races, with dark wing lings and a strongly barred tail. In the juvenile plumage, the nominate race has a strongly buffy headed and has underparts that are flecked and spotted. The crest tends to be longest in this race, with common measurements of 10 to 14 cm (3.9 to 5.5 in) in length, therefore the race is commonly referred to as the crested hawk-eagle. [3][9] It is one of the two larger subspecies. Wing chord length ranges from 405 to 442 mm (15.9 to 17.4 in) in males and from 448 to 462 mm (17.6 to 18.2 in) in females. In both sexes, the tail commonly measures 280 to 300 mm (11 to 12 in) and tarsus from 102 to 110 mm (4.0 to 4.3 in). [3]
  • N. c. ceylanensis: This race is endemic to Sri Lanka but some authorities also include Travancore in the southern tip of India as part of this race's range. [3][12] This race has a proportionally longer crest on average than the nominate race, with a similar crest length to it at about 10 cm (3.9 in). It is monomorphic as is the nominate race, averaging paler and less streaky, but a similar appearance has been noted to birds from southernmost India are rather similar in appearance. The differences represented in this race from the nominate race are largely clinal. It is rather smaller than the nominate race. Wing chord length ranges from 351 to 370 mm (13.8 to 14.6 in) in males and from 353 to 387 mm (13.9 to 15.2 in) in females. [3][13] Furthermore, in both sexes tail length is from 229 to 266 mm (9.0 to 10.5 in) and tarsus length from 89 to 97 mm (3.5 to 3.8 in). [6][13][14]

Crestless changeable hawk-eagle

  • N. c. limnaeetus: This race is found through the Himalayan foothills from Nepal, northeast India, via Burma to much of southeast Asia including the Malay Peninsula along Wallace Line to Philippines and the Greater Sunda Islands. This race can appear similar in size and build to the nominate race but unlike it is rather polymorphic and this is the most widely found of subspecies. This race's polymorphism is the source for the species being referred to as the changeable hawk-eagle. [6] The pale morph of this race is still darker than the nominate race found further south in India. However, pale morphs from the Philippines tend to have a paler head and neck. Characteristically, this race is heavily streaked below, while juveniles look quite different as their head and underparts are largely white. Dark morph individuals tend to be chocolate-brown all over, although the tail base might appear lighter in flight. [3][14] Some birds of this race do have a vestigial crest of merely 1 to 3 cm (0.39 to 1.18 in) in length but many appear to completely lack the crest. This race is generally similar in size to the nominate race but is more variable in size over its large distribution within the southernmost island birds averaging smallest while those found in the Himalayan foothills are arguably the largest hawk-eagles known in the species. Wing chord length ranges from 380 to 430 mm (15 to 17 in) in males and from 405 to 462 mm (15.9 to 18.2 in) in females. In limited samples, tail length was reported as 240 to 278 mm (9.4 to 10.9 in) and tarsus length from 100 to 103 mm (3.9 to 4.1 in). [15]
  • N. c. andamanensis: This race is found in the Andaman Islands. The subspecies is darker than the nominate subspecies and more similar to N. c. limnaeetus in hue but does not appear to have a full dark morph as is known in that race. Andamanian juveniles tend to have a rather white head and underpart colour. A crest may variably be present but is usually only up to 5 cm (2.0 in). This race is small, a little smaller even than N. c. ceylanensis. Wing chord length ranges from 330 to 375 mm (13.0 to 14.8 in) in males and from 358 to 377 mm (14.1 to 14.8 in) in females. [3][14]
  • N. c. vanheurni: This race is native to Simeulue Island. It is similar in appearance to N. c. limnaeetus, but apparently lacks a dark morph. The subspecies is also much less heavily blotched black on its whiter looking breast and never bears a crest. It is the smallest accepted subspecies of the changeable hawk-eagle, considerably smaller than N. c. limnaeetus. Wing chord was measured as 312 mm (12.3 in) in a single male and 329 to 337 mm (13.0 to 13.3 in) in a small sample of females. [3]

The changeable hawk-eagle is a largish but slender eagle. They fall near the middle of sizes among the currently accepted species in the genus Nisaetus. As in most birds of prey, females are larger than males with an average overall size difference of 7% but this can individually range to an 18-22% difference, with island races apparently thought to be less dimorphic on average. Size is quite variable and total length has been reported in the past to vary from 51 to 82 cm (20 to 32 in) and wingspan from 100 to 160 cm (3 ft 3 in to 5 ft 3 in), however these figures appear to include the much more massive hawk-eagles from Flores that are currently considered their own separate species by modern authorities. [3] [16] Nonetheless, total lengths of up to 77 cm (30 in) have been listed for N. c. limnaeetus in Nepal. [17] Ali & Ripley (1978) estimated these average total lengths for the following subspecies: N. c. cirrhatus at 72 cm (28 in), N. c. limnaeetus at 70 cm (28 in) and N. c. andamanensis at 61 cm (24 in). [14] Legge (1880) measured the length of Sri Lankan changeable hawk-eagles (N. c. ceylanensis) without including the beak as 55 to 60 cm (22 to 24 in). [13] The average length of birds from the Philippines (N. c. limnaeetus) was measured as 58.4 cm (23.0 in) in males and 64.9 cm (25.6 in) in females. [18] Weights in this species have been reported from 1.2 to 1.9 kg (2.6 to 4.2 lb) but the source of this is unclear and it probably underrepresents the size variation known to occur in the species. [6] [16] [19] The only precise body masses known for the species are derived from the Philippine population, where males were found to average 1.36 kg (3.0 lb) while females averaged 1.6 kg (3.5 lb) but they could weigh in excess of 1.81 kg (4.0 lb). [18] [20]

Adult changeable hawk-eagles are typically dark brown above and boldly streaked below with a strong bill, a variably sized, often floppy crest or no crest, rather short wings, a quite long, thinly-barred tail and long feathered legs. This species tends to perch “bolt” upright, and may perch in various places from somewhat secluded spots to also quite open area as well. [3] [6] When perched, their wings reach only about one-third to halfway down tail. Pale morph adults are mainly dark brown above with very faint paler edges (usually only conspicuous on the wing-coverts). They tend to have an evenly black-streaked and somewhat rufous-tinged head and neck, with a blackish crest (if present). The tail tends to be paler brown than the back with a thin whitish tip, a broad, blackish subterminal band (both the whitish tip and the subterminal band are also visible from tail underside) and 3 to 4 narrower, brown and often rather obscure bars. On the pale morph hawk-eagle's underside, the base colour is white to buff overlaid with bold black to dark brown streaking the streaking tends to be more subtle on abdomen but more obvious on the legs. Beyond the typical pale morph, some subspecies but especially N. c. liminaeetus tend to have a further intermediate and a dark morph. The intermediate morph is somewhat similar to pale morph adults but is heavily grey-brown below with little to no paler base colour showing and more obscure streaking, with the area from belly down to the crissum usually being unpatterned. Meanwhile, the dark morph adult can range from all dark chocolate brown to almost pure black with variable browner edges, relieved only by the greyish inner half of tail as well as some greyish tail bars. [3] [6] Most juvenile changeable hawk-eagles are dark brown above but with far more conspicuous white edges on mantle and wings than the adults, in some cases, the median coverts are largely white and greater and even lesser coverts are largely scaled with white. The juvenile has a light brown tail with about seven thin dark bars and a whitish tip. The young hawk-eagle's head varies from buff with white-tipped black crest (as is the case in peninsular India and Sri Lanka) through entirely whitish, but almost always the young birds are spotted and streaked with black or dark brown about the rear crown and nape. As is the head, the underparts are variable with juveniles in much of India and in Sri Lanka showing thin brown streaks on chest or small spots on breast, with obscure tawny barring on thigh, legs and crissum. Juveniles elsewhere are often nearly all pure whitish below. By the time the young hawk-eagles reaches their 2nd to 3rd year, they tend to show less white above and more brown or black below. Their tail starts to molt to resemble that of adults in the 3rd year but in the 2nd year in N. c. limnaeetus (or at least in Philippines). Changeable hawk-eagles may attempt to breed at 3 years of age but full adult plumage is not obtained until the 4th year. [3] [6] [20] Adults have yellow to orange yellow eyes, while those of the juvenile are grey-brown to pale greenish. Adult have a cere that's grey to pale greenish yellow and juveniles’ ceres are dull greyish, while all ages have yellow feet. [3]

In flight, the changeable hawk-eagles is a large raptor with a prominent head, rather short rounded and broad wings, longish squarish or rounded tail, but has somewhat slenderer wings and straighter trailing edges than sympatric species of hawk-eagles. The species tends to fly with a fast agile flight, showing powerful shallow beats interspersed with glides on flat or bowed wings with their carpals well forward (above level of bill) and primaries swept back. When soaring, the wings are gently lowered or sometimes held level, with the carpals again well forward. In pale morph adults in flight, their hand in flight may be variously dark brownish buff (as in peninsular India) to a much paler buff or whitish. On the flight feathers, the area from wingtips extending to the primary and secondary feathers often have blackish barring, forming ragged lines from the carpals to rear axillaries with variable other dark marks elsewhere. Adult intermediate morph hawk-eagles have similar flight feathers but have grey-brown underparts with a less distinct, contrasting underpattern. Meanwhile, in both juvenile and adult dark morph, the blackish-brown colour of the body extends to the hand but the base of their tail, their primaries and, less so, their secondaries are a much paler, contrasting grey with streaking similar to other changeable hawk-eagles. Typical juveniles show large areas of whitish streaking or mottling seen from above in flight. Juveniles from much of India and Sri Lanka show extensive darker tawny but obscure barring above and below, while other races are much whiter. Much like adult, the juvenile has dark tips to primary and greater coverts produce thin ragged diagonal bars but the barring tends to be thinner. [3] [21]

Voice Edit

The changeable hawk-eagle is often largely silent but in breeding season it may readily call, both from their perch or on the wing. Like many diurnal raptors, their calls are a form of high-pitched scream. The shrill ringing and loud call of the changeable hawk-eagle is various described in pattern of yeep-yip-yip-yip, rising kwip-kwip-kwip-kwee-ah and penetrating klee-leeuw (for birds from the Sunda islands). Ascending kri-kri-kri-kree-ah and kreeee-krit with much stress on the elongated first syllable are similar. From western birds from India and Sri Lanka, the call is a slightly different ki-ki-ki-ki-ki-ki-ki-keee, beginning short, rising in crescendo and ending in long, drawn-out scream. In northern India and Malaysia, the calls of this species have variously been compared to those of the Eurasian curlew (Numenius arquatus) and the crested serpent eagle (Spilornis cheela). [3] [6] [22]

Confusion species Edit

The changeable hawk-eagle is almost always the most common and/or most widely spread Nisaetus species anywhere in their range. Their distribution overlaps with the entirety of the distribution of the (newly recognized) Legge's hawk-eagle (N. kelaarti), most of the range of the Javan (N. bartelsi), Blyth's (N. alboniger) and Wallace's hawk-eagle (N. nanus) and partially overlaps with the ranges of the mountain hawk-eagle (N. nipalensis), the Philippine hawk-eagle (N. philippinus) (on Mindoro and possibly Palawan) and Pinsker's hawk-eagle (N. pinskeri) (on Mindanao). Only two species of the genus Nisaetus are outside the changeable hawk-eagle's normal distribution (including their own former subspecies, the Flores hawk-eagle). [1] In range with most other Nisaetus species (such as the islands or mainland of southeast Asia), the changeable hawk-eagle is more likely to be almost crestless. Other species tend to have proportionately broader wings with more bulging secondaries, relatively shorter tails and, as adults, more barred underbody and unique tail patterns. Adult colour patterns can range from somewhat different to boldly distinct (especially in the black-and-white Blyth's hawk-eagle). Juveniles tend to be more difficult to distinguish but usually most other Nisaetus have less white showing than relevant changeable hawk-eagles and the changeable tends to show a slightly stronger V while in flight. The mountain hawk-eagle, Flores hawk-eagle (which is the only hawk-eagle in its small-island range) and Legge's hawk-eagle, in decreasing magnitude of size, are all are larger and bulkier than the changeable hawk-eagle whereas other Nisaetus species are smaller to varying degrees, distinctly so in the Wallace's hawk-eagle and Blyth's hawk-eagle. [3] [23] [24] As many honey buzzards are thought to mimic more powerful raptors to protect themselves from predation, the crested honey buzzard (Pernis ptilorhynchus) is thought to mimic the general appearance of Nisaetus hawk-eagles but has a distinctly smaller head and longer and narrower wings than changeable hawk-eagles. Adult crested honey buzzards are barred but the juvenile is streaked rather like the changeable hawk-eagle, however if seen well the honey buzzard generally looks much more solidly orange-buffy as a base colour rather than whitish below. The flight actions of the honey buzzard are also distinct, with a more robotic even flap during flights. [3] [23] [25] Juvenile crested serpent eagles, which are unlikely to be mistaken for the changeable other than at a distance and in flight, appear chunkier and less rangy with a bigger head, slightly longer wings and a substantially shorter tailed with fewer bars (these differences in proportions are generally applicable to various island serpent-eagle species that may be found with changeable hawk-eagles as well). Juvenile rufous-bellied eagles (Lophotriorchis kienerii) are rather smaller and more compact with a relatively longer winged and shorter tailed appearance. The rufous-bellied juvenile when compared to the juvenile changeable is generally purer white looking below which contrasts more strongly with their sparse blackish streaks. Dark morph changeable hawk-eagles may be confused with the similarly-sized but even more slender black eagle (Ictinaetus malaiensis). However, the latter is much longer winged with distinctly pinched-in bases, a uniformly dark tail and has small light feather bases only to primaries. Also dark morph can be told from dark morph booted eagles (Hieraeetus pennatus) by the latter being rather smaller, much shorter tailed and having relatively longer and more rectangular wings. Dark morph booted eagles are also grey-brown or cinnamon from below on the tail and have pale wedges on the underside of the primaries. [3] [6] [21] [23]

The extensive range of the changeable hawk-eagle includes much of the Indian subcontinent and southeast Asia. Their distribution includes nations and areas such as Sri Lanka, Himalayan foothills (Garhwal to Assam), southern Nepal and Bhutan east through Myanmar, Burma, western Laos, southern Vietnam, Cambodia, Thailand and peninsular Malaysia. In India, they may found almost continuously from the peninsular tip north to Rajasthan, Uttar Pradesh, Bihar and Odisha. Its island distribution includes the Andamans, Sumatra (including Simeulue and Mentawai off the west side and Riau, Bangka and Belitung off of the east), Java, Borneo and the western and southern Philippines (including Palawan, Calamians, Lubang, Mindoro, Mindanao and apparently recently Bohol). Like most tropical raptors, the changeable hawk-eagle is largely residential, but stragglers from peninsular India have roamed to northeastern Burma and southeastern Thailand and some records in the Lesser Sunda Islands (Bali, Palau and Lombok) may be from vagrants from Java. [1] [3] [6] [23] The species may live in savannah woodland, cultivation with trees, timbered watercourses, tea plantations, forest villages and even suburban edge. Beyond these often degraded haunts they range as well as any of the more forest-clinging Nisaetus into fairly open or less dense parts of undisturbed vast evergreen or deciduous forests (their deciduous ranges mainly occurring in India and the Sunda islands), but also second growth and wetlands. In elevation, they may be found anywhere from sea level to 2,200 m (7,200 ft) but mainly live below 1,500 m (4,900 ft). [3] [6] [26] [27] It is not uncommon in foothills of Sri Lanka but again does not usually exceed 1,500 m (4,900 ft) elevation there. [28]

Changeable hawk-eagles are at home in a variety of wooded and semi-open habitats. Their physical form and flight style is typical of forest-dwelling raptors in general and is often compared to the features of true hawks or Accipiters in particular larger species such as goshawks. Like most other forest raptors, changeable hawk-eagles (and Nisaetus species in general) have a long tail, short broad wings and relatively long but powerful legs, all of which impart greater maneuverability and quicker strike times in denser wooded hunting grounds than other raptorial body plans. The common name hawk-eagle is apparently in reference to their similar adaptations to true hawks. [6] [29] Even compared to the variable prey of large goshawks, the prey selection of changeable hawk-eagles appears to be somewhat indiscriminate and opportunistic. [6] [30] Unfortunately, compared to tropical raptors from the neotropics and especially Africa, the life histories of raptors from tropical Asia are generally quite poorly-known, even in the case of easily observed raptors such as changeable hawk-eagles. [31] [32] Therefore, what is known of changeable hawk-eagles dietary biology is largely drawn together based on reliable eye-witness and anecdotal accounts, photographic evidence and wide-ranging bird census surveys, rather than direct, extensive study. [6] The changeable hawk-eagle can show a slight preference for birds as prey, but also freely takes various mammals, reptiles and some other vertebrates whenever they opportune upon them. [3] [6] Although little quantitative analysis has gone into their dietary habits, many prey items taken are relatively small. On the other hand, Brown & Amadon (1986) description of this species as “not a very rapacious bird” is not entirely justified as extremely large prey relative to the hawk-eagle's size may also be readily taken. [6] [20] [33] Like many tropical forest raptors, they are primarily ambush predators who use concealing foliage to still-hunt from hidden branch or open branch with a leafy background, pouncing fast to take most of their prey on the ground. Like goshawks, changeable hawk-eagles often perch-hunts which are short, low-level flights from perch to perch interspersed with brief pauses, during which they scan for potential prey. Perch-hunting lends them the greatest success when hunting birds that they will capture in the trees. [3] [6] At least a few cases have been observed of changeable hawk-eagles watching for and then dropping on prey directly from their own nest. [6]

One of the only general analysis of the quantitative food preferences of the changeable hawk-eagle (although detailed prey analysis, including prey species, was not specified), was a study of this species in contrast with five other raptor species in the Maharashtra state of India. This showed that they had a preference for birds as prey, with nearly equal number of birds classified as small or large making up nearly half of their diet in 14 active territories. Furthermore, their prey selection was found to be somewhat similar by class to that of Bonelli's eagle (Aquila fasciata), an eagle of much more open and rocky habitats, but the changeable hawk-eagle took the highest class diversity of prey of any of the six raptors studied and was the only one to hunt near heavily wooded areas. [34] Primary prey by class differed in West Java, where 62% of prey selected was reptiles, 24% birds and 12% mammals. [35] Elsewhere in India, prey selection at the nest showed what prey species were selected by changeable hawk-eagles but lacked any quantitative data or studies on prey biomass. One study in Gujarat showed several rather small prey species largely being taken such as the Indian chameleon (Chamaeleo zeylanicus), Oriental garden lizard (Calotes versicolor), other lizards, common myna (Acridotheres tristis), red-vented bulbul (Pycnonotus cafer), other birds (including unidentified parakeets and gamebirds), Indian bush rat (Golunda ellioti) and a palm squirrel. The identified prey would vary in size only from 35 g (1.2 oz) for a garden lizard to 117 g (4.1 oz) for a myna with the small lizards and chameleons reportedly the most often delivered prey. [6] [36] [37] In Mudumalai National Park, only three prey types were specified to genera which consisted of black-hooded oriole (Orolus xanthornus), common bronzeback snake (Dendrelaphis tristis) and an unidentified giant squirrel. [6] Not all nests have relatively small prey, as one nest in northern India showed a prey composition of red junglefowl (Gallus gallus), large woodpeckers such as flamebacks and larger parakeets. [6] Alongside various junglefowl and the domestic chicken derived from them, virtually any gamebird seem to be nearly ideal prey for changeable hawk-eagles and several species, including peafowl, bush quail, spurfowl and francolins, are known to be hunted, including both young and adults. [3] [6] [20] Many other birds with partial terrestrial habits seem to be taken quite widely including various pigeons and doves, rails and other water birds. [35] [38] [39] [40] [41] [42]

The upper size limit for changeable hawk-eagle prey seems to be fairly liquid and the species is quite the equal of various other booted eagles in making bold attacks on prey of their own size or larger. [6] [33] Many of the mammals reported as preyed upon by changeable hawk-eagles are quite large. Mammalian prey taken as adults has included hispid hares (Lepus hispidus) with a median estimated weight of 2.35 kg (5.2 lb), Indian hare (Lepus nigricollis) with a median mass of 2.7 kg (6.0 lb), 1.3 kg (2.9 lb) Indian flying fox (Pteropus giganteus) and nearly any species of giant squirrel, which can vary in weight between 1.1 and 3 kg (2.4 and 6.6 lb). [6] [33] [43] [44] Even more impressive accounts and photos show that changeable hawk-eagle can hunt and kill adult mammals with formidable defenses such as felids and primates, although it cannot be ruled out that they will usually attack infirm or injured specimens rather than healthy ones. Furthermore, most accounts of attacks on Old World monkeys show juveniles are by far the most vulnerable members of their troops to hawk-eagle attacks. Cases of either verified, likely or potential predation have been reported on northern pig-tailed macaque (Macaca leonina), crab-eating macaque (Macaca fascicularis), toque macaque (Macaca sinica) and lion-tailed macaque (Macaca silenus), including specimens potentially to weigh up to an estimated 6 kg (13 lb). [33] [45] [46] [47] A case of predation was photographed by a changeable hawk-eagle on an estimated 1.9 kg (4.2 lb) juvenile banded langur (Presbytis femoralis) while possible cases have been reported of predation on juveniles of other langurs as well as additional larger primates such as gibbons and proboscis monkeys (Nasalis larvatus). [33] [48] [49] [50] [51] [52] While their predator-prey relationship is even more nebulous, the peculiar, smaller but toxic nocturnal primates known as slow lorises are known to fall prey as well to changeable hawk-eagles. [53] [54] There are several accounts of predation by changeable hawk-eagles on domestic cats (Felis silvestris catus), though largely kittens, in addition to a case of a large adult jungle cat (Felis chaus), with an estimated median weight of 7.3 kg (16 lb), being attacked and killed by one of these hawk-eagles. [6] [33] [55] Apparently, the changeable hawk-eagle is also counted among the predators of young calves of Indian gazelles (Gazella bennetti) as well. [56] Adults of large monitor lizards of a few species may be also included in their prey spectrum. [6] [57] [58] Impressive avian kills have included adult Indian peafowl (Pavo cristatus), of an estimated weight of up to 4 kg (8.8 lb), and the species is considered a threat as well to the similar green peafowl (Pavo muticus). [33] [59] [60] Attempted predation on both 4.2 kg (9.3 lb) adult and young giant ibis (Thaumatibis gigantea) have been recorded but all known attacks were unsuccessful. [61] Cases of scavenging on carcasses of various deer and monkey have been reported as well, in one case a hawk-eagle was filmed apparently dominating and displacing an adult yellow-throated marten (Martes flavigula) from a carcass. [62] [63]

Interspecies predatory relationships Edit

The habitat selection and overall distribution of the changeable hawk-eagle is largely concurrent with other largish raptors such as the crested serpent eagle and the crested honey buzzard, apparently the three species are largely tolerant and non-aggressive towards each other, perhaps surprisingly given the otherwise aggressive habits of hawk-eagles. Unsurprisingly, these species have quite discrepant ecological niches, especially in terms of their dietary habits. [6] Although nest predators are probably profuse, parent changeable hawk-eagles are likely to aggressive displace most potential threats. No verified accounts of predation are known in the wild and the species often likely fulfills the role of an apex predator. [6] They are presumably able to persist alongside larger cousins such as mountain hawk-eagles and with Legge's hawk-eagle by focusing more so on reptiles and birds rather than the mammalian prey likely preferred by the larger species (as well as perhaps focusing primarily on a smaller class of prey), although it is somewhat more adaptable in habitat than both other species. [6] [64] They are also found living alongside the much larger Philippine eagle (Pithecophaga jefferyi) and are likely to similarly take smaller prey and avoid direct encounters with the much less numerous giant eagle. [18] In turn, changeable hawk-eagles are likely avoided in encounters with smaller forest raptors such as other, smaller Nisaetus species, which often focus slightly less on birds than the changeable, and Accipiter hawks, which all subsist largely on rather smaller classes of prey. [6] [18] [65] Apparently, changeable hawk-eagle are considered likely predators (on fledglings?) of the slightly smaller Indian spotted eagles (Clanga hastata). [66] However, on the contrary, one case of predation was reported in captivity when a barred eagle-owl (Bubo sumatranus), which is found in the wild with changeable hawk-eagles in southeast Asia, killed a changeable hawk-eagle in an aviary. [67]

The changeable hawk-eagle is, like many raptorial birds, a largely solitary bird otherwise but during breeding, stays in a dedicated pairs that often mate for life. Each pair engages in a territorial display over the fringes of their home range. This aerial display is usually engaged in by a male but sometimes the female or both members of the pair will engage in displays, often starting with their wings and tail arched upwards in exaggerated poises. During the display, the shoot up vertically and nose-diving or stooping, if the rival hawk-eagle continues to engage the defending individual, they will fly at each other at "lightening speed" doing a complete loop-the-loop turn in air. They often call loudly throughout the display. [3] [6] [14] The breeding season of changeable hawk-eagles falls from November to May in southern India, peaking January–March, while it is more confined to January–April in the more temperate climate of the Himalayan foothills. The breeding season from India is comparable in Sri Lanka but is slightly more prolonged in the latter country, continuing at times into June. However, peak laying dates fall earlier, around January–February, in Sri Lanka. [3] [20] In the equatorial Greater Sunda islands, eggs have been recorded in 8 different months at any time from December to October with peak activity falling usually between February and August. Apparently, the highest volume of eggs laid here fall in two separate periods, February–March and July–August. Thus, the breeding season is more elastic in tropical forests areas but in northern part of range the breeding season centers around the cooler dry season. [3] [20] This species builds a largish stick nest. Typical dimensions of their nest is 95 to 105 cm (37 to 41 in) across while nest depth can range from 35 to 120 cm (14 to 47 in) the latter after repeated uses and additions. [3] [20] Some nests are very large relative to the size of these eagles. One nest reached an diameter on the inside of 1.3 m (4.3 ft) and a circumference of 3.45 m (11.3 ft). [6] Active nests are lined with green leaves. Both members of the pair participate in building new nests and take part in repairs. [3] [20] Nests are often solidly built and resilient, more so than those of other medium-sized eagles, against high winds and monsoons. [6] Nest height is often from 6 to 50 m (20 to 164 ft) in the crown or high fork of a large tree, but is usually not less than 12 m (39 ft) off the ground. [3] [20] Nest height in the Indian subcontinent was typically around 12 to 25 m (39 to 82 ft), averaging 17 m (56 ft) in the Shoolpaneshwar Wildlife Sanctuary and 19 m (62 ft) in the Indo-Gangetic Plain, and could be in a wide diversity of trees. [6] Nesting sites are often near a stream, or otherwise perhaps near a ravine with wide view but sometimes varies from deep forest to isolated trees on village edges. [3] In the peri-urban green spaces of Singapore, changeable hawk-eagles nested mostly on Albizia trees, which are among the fastest-growing and tallest trees in these secondary forests. [68] The parents tend to allow closer approach by humans when living in vicinity of villages. [20]

Only one egg is known to be laid by changeable hawk-eagles. The egg tends to be coarse and glossless, largely white but sparely and faintly speckled or blotched with light reddish. Egg sizes were reportedly measured in the nominate subspecies (sample of 40) as ranging from 65.3 to 73 mm (2.57 to 2.87 in) in height with an average of 68 mm (2.7 in) by a diameter of 49.9 to 53.3 mm (1.96 to 2.10 in) with an average of 52 mm (2.0 in). In the race N. c. ceylanensis, a sample of 24 eggs averaged 61.3 mm × 49.8 mm (2.41 in × 1.96 in). In N. c. limnaeetus from northern India, 18 eggs averaged 69.8 mm × 51.6 mm (2.75 in × 2.03 in). In the same subspecies, eggs from Java and Borneo ranged from 61 to 68.8 mm (2.40 to 2.71 in) in height and from 50 to 54 mm (2.0 to 2.1 in) in diameter. In the race N. c. andamanensis, the average was reportedly 62.2 mm × 50.1 mm (2.45 in × 1.97 in) but the sample size is unknown. [20] Apparently, the female alone incubates, for a period estimated at about 40 days. [3] [20] After the nestling hatches, the female will brood intensively for about 25 days. [6] An Indian nestling was found to weigh 300 g (0.66 lb) at 14 days and grew to 450 g (0.99 lb) by 20 days, having developed a vocabulary of cheep notes to express hunger and alarm. The eaglet may be preening, standing more and wing flapping by 4 to 5 weeks old, and may also be encouraged to eat at by its mother, however consuming a single food item may take up to 6 hours at this point. [6] [20] At 35 days, the nestling may be brooded progressively less and feather and body size growth accelerates. Within in a couple weeks, prey is delivered (often by both parents at this stage) to nearby branches rather than directly to the nest with the parents calling as they approach, apparently encouraging the young eaglet to venture out of the nest. [6] [20] By 52 days of age, the eaglet is fully-grown but does not fledge until about 60–68 days. [3] [6] The total nest dependency was recorded as 81 days in India. [6] However, the total breeding cycle was recorded as lasting about 112 days in West Java. [35]

The changeable hawk-eagle apparently ranges over 13 million square kilometers across its range. An average of only 1 pair to every 1,200 km (750 mi) of its distribution would put the population well into five figures but their density is likely rather higher. [1] [3] This species is an exceptionally adaptable one not only by the standards of its genus but also by the standards of its subfamily. While deforestation has depleted the populations of their fellow Nisaetus species, resulting in four being classified as Endangered species, the changeable hawk-eagle has been shown to be remarkably resilient in the face of cutting and habitat degradation. This trend, holding steady in population or even increasing while other hawk-eagle species have declined, has been reported in the Indian subcontinent, Malaysia, Java and the Philippines as well as elsewhere in southeast Asia. [18] [69] [70] [71] [72] In Java, the changeable hawk-eagle was found to persist in all seven habitat types available on the islands, whereas the Javan hawk-eagle was confined to only four habitat types: the deeper, primary forested areas. [26] However, their adaptability can be overstated and this species requires tall trees (though secondary growth forest is acceptable), appropriate habitat composition and ample prey populations to flourish. It is likely they can persist in most variety of high grade forestry and urbanization but complete deforestation is the only major threat to this species. [3] [6] A more secondary concern, but potentially depleting populations in India at least, is that it will not infrequently hunt chickens (especially during breeding when such easy prey is hard to resist), which has in turn resulted in changeable hawk-eagles being locally persecuted. [6]

Red-tailed Hawk Size

Data for length, wingspan and weight below (males and females combined) is from A Photographic Guide to North American Raptors (Wheeler & Clark 1995). We highly recommend this book for anyone interested in raptors.

Length: 17-22 inches (45-55 cm)

Wingspan: 43-56 inches (110-141 cm)

Weight: 710-1550 grams (18-53 oz)

Red-tailed Hawk Wing** (Friedmann 1950 N males=35, N female=27)
Males: mean 369.6 mm (337-396)
Females: mean 388.8 mm (370-427)

Red-tailed Hawk Tail (Friedmann 1950 N males=35, N female=27)
Males: mean 215.6 mm (197-240)
Females: mean 230.3 mm (214.5-254)
Red-tailed Hawk Weight (Snyder and Wiley 1976)
Males: mean 1028 g (n=108)
Females: mean 1224 g (n = 100)

We have found (as have others) that Western Red-tailed Hawks have longer Wings and Tails than Eastern birds (See data below).

The data below were collected while we were doing research on Red-tailed Hawks. Male and female data are combined.

Red-tailed Hawk un-flattened Wing Chord*
Eastern: mean 378.3 mm (350-406)
Western: mean 403.5 mm (370-430)

Red-tailed Hawk Tail Length
Eastern: mean 210.0 mm (185-250)
Western: mean 238.5 mm (211-285)
Western Red-tailed Hawk Weight
mean 1011.6 g (595-1612)

**Wing from Friedmann data assumed to be un-flattened wing chord.
*Wing Chord is measured from from the wrist to the tip of the longest primary feather on one wing. The primary feathers have a natural camber (bend), and can be measured flattened or un-flattened.

Red-tailed Hawk Diet: Approx. 85% small-medium sized mammals (mice, voles, rabbits, hares and squirrels), as well as small-medium sized snakes and lizards. They are also known to eat insects, birds and bats. Watch Red-tailed Hawks catch bats in BBC video below.

I witnessed a soaring Red-tailed Hawk snatch a small bird out of the air that flew too close (probably an American Goldfinch or Pine Siskin). The Red-tail stooped after the bird while it spiraled downward and grabbed it. The Red-tail then resumed soaring and ate the bird "on the wing". There were at least 40 other observers at a Hawk Mountain (migration observation site) that witnessed the event that day.

Red-tailed Hawk Nest: Usually 28 - 30 inches in wide, with an inner cavity of 14 - 15 inches diameter and 4 - 5 inches deep. The nest is made of sticks and twigs (usually one-half inch thick or less). The nest cup is lined with strips of bark and fresh greenery, usually an evergreen sprig.

The nest is usually placed in the crotch of a large tree or on a cliff ledge at least 25 feet above the ground. Most nests are 15-70 feet high.

I found and climbed into a Red-tailed Hawk nest that was 92 feet up in the broken top of a white pine to band the chicks. Their nest sites usually have a commanding view of the area. I also banded a chick in a Red-tailed Hawk nest that was on a cliff ledge about 100 feet above the ground.

Nest Construction usually begins in February or March.

Red-tailed Hawk Eggs: The clutch almost always consists of 2 eggs in the Eastern U.S. and Canada and 3-4 (and even 5) in the Central and Western parts of North America.

Average size: 59 X 47 mm. (Bent, 1937)

Eggs are usually dull or dirty white (sometimes a pale bluish or greenish white). Eggs can be un-marked, but usually have some reddish to brownish markings or blotches that may be either faint or dark.

Egg laying usually begins in March or April. Eggs are usually laid 30-48 hours apart.

Red-tailed Hawk Incubation period: 28-30 days for each egg, but since incubation usually begins with the first egg, an additional one or two days is needed for each additional egg. A two-egg clutch may be incubated 30-32 days and nests with 3 eggs may be incubated for 32-34 days.

The first egg will hatch one or two days before the second egg, and a third egg would hatch another day or two later.

Red-tailed Hawk Fledging: Chicks usually make their first flight between 40-46 days after hatching and fledging usually occurs between late May and Mid July.

Longevity Record: 28 Years and 10 months based upon known age of a wild Red-tailed Hawk at banding and subsequent band recovery (Data from Bird Banding Lab (Klimkiewicz 2008).

Red-tailed Hawk Migration: Red-tailed Hawks migrate from the Northern parts of the breeding range during late Autumn. There are many raptor migration sites where Red-tailed Hawks can be viewed during Migration (See Raptor Migration Sites).

Sub Species: There are six races or subspecies of Buteo jamaicensis in North America and 8 additional subspecies in the Caribbean, Central America and Mexico see Red-tailed Hawk Subspecies here.

To Feed or Not To Feed

Many conservation organizations and governments not just support feeding wildlife but depend upon the funds raised from selling bird food or the taxes generated. Feeding wild birds is big business. It is also a practical business. Undoubtedly the only way our degraded city or urban habitats, with their natural grasses, shrubs and trees replaced by roads, houses and gardens, can house any wildlife, and particularly birds, is for humans to replace some of the items we have destroyed. The artificial garden plants don’t always produce the same seeds, pollens or insects that feed our native birds.

The human supplemental feeding of these birds with bought seeds, suet and honey-water etc. provides many native species with the key items destroyed and missing in the urban environment — the food items that were removed by human development. Of course some feeders also attract sharp-shinned and coopers hawks, merlins and peregrine falcons, assisting other elements in the food chain indirectly.

That feeding wildlife is a generally accepted principle and practical assistance to wild birds does not mean that supplemental feeding does not have downsides. These negative issues are certainly of concern and will be addressed later but they are relatively minor compared to the benefits. In the big picture, the destructive nature of humans, their total or even partial disruption of native bird or general habitats can and should be supported by our attempts to hold and then bring back species by effectively recreating suitable habitat. There seems universal agreement here.

Some conservationists, particularly the scientific community and the government agencies they represent have “had to” learn the “double-speak” of politicians and lawyers. They have had to advocate for the extreme position because we have never learned how to enforce laws cloaked in the reasonableness of “its ok here, but not there” approach that must govern nature. Laws don’t seem to cover this approach. For laws to be effective they seem to require black and white interpretations. You either can do it or you can’t do it – always and not just ‘sometimes’. Laws don’t work well if you have to qualify and debate values and results on each pertinent issue. But natural systems are complex, interrelated systems that at specific levels don’t effectively respond to yes or no applicable for bureaucrats. Natural systems demand commonsense.

It is the humans who always try and abuse the spirit or intent of the law, to gain some specific personal advantage, who cause the abuse. So we are left with the government policies, and sometimes laws, that cover the administrators’ backsides, give them some legal grounds if abuse is being perpetrated but, under other commonsense circumstances are simply ignored. You simply can’t ask somebody who must support the rigidity of rules that support law, to now discuss reason and exception. It is not feasible. This is not administrative commonsense. They cannot speak of reason. They must speak of ‘right or wrong’. You know their answer before you ask the question. So be careful of whom you ask the question. Don’t put them on the spot.

This whole issue of feeding or not feeding eagles is all about this incongruous “double-speak” system of rules, come laws. I accept that. Yes, please buy food to feed wildlife yes we derive revenue for our organizations and even for our governments from these sales yes this is likely the only way to keep many species of birds in existence, let alone get a new hold on marginal but improving habitat but “no you shouldn’t feed wildlife.” !

The real issue is don’t ask certain people — the ones paid to write the rules, the question unless you want to hear the double-speak answer. It is as simple as that.

This is not criticizing the government biologist or spokespersons. These are the rules they are forced to work under. I have never known a conservationist or biologist who would not help wildlife, from planting a native shrub, to supply food to their birdfeeder, to removing a roadkill farther from the traffic so the second and third scavenger is not also killed.

Every — well make that almost every — conservationist out there is trying to improve wildlife habitat: to preserve the small existing natural habitats from further destruction, and is trying to improve the vast majority of the world’s landscape already disrupted or totally destroyed by people, their roads, the houses and industry and particularly their farms. Planting native grasses, shrubs and trees in our gardens and parks is a great start. Supplementing the lost old growth nest holes with nest boxes or suitable nesting tree structures or ledges on buildings is all wonderfully helpful. Putting out the variety of seeds, suets and nectars supports the wild birds finding more essential elements of their habitat — the food component. All this is good and acceptable — ok — with some cautions that we will discuss later! This is the commonsense position, not the ‘double-speak’ position required to support laws.

So how do we get into this ‘inflamed discussion, this righteous indignation, this emotional “I care more than you” standoff when it comes to discussing feeding wildlife. Well obviously it is because we care about nature, we care about our backyard birds, we care about our eagles. Most of us have come to this forum with little background on eagles — or wildlife. Marvelous! That is the very reason for the existence of this Cam site!. The CAMs give insite into the marvelous and confusing ways of wildlife and hopefully invite discussion. Our site is then doing its job. Some people have taken strong positions for or against something. It is great you care. I love it.

Some people keep looking for more information — that is even better. Some people will have had experience with backyard feeders, with watching wild birds at natural sites, some even will have had the experience of seeing several hundred or even thousands of eagles gather at salmon streams or other natural disasters where their 100,000’s of years of evolution of scavenging tells them to ‘come get this free but temporary dinner’. Some in their search have found the positions of authorities, the ‘double-speak’ extreme positions required for enforcing laws and have not understood the practical needs and applications of encouraging animals to survive and re-occupy old habitats. The ‘double-speak” is there so laws can be enforced when abuses take place. At the practical level commonsense must prevail. Those are not words that can or should come from authorities but these are the words that govern concern for living creatures.

Some Eagle Background:

Bald eagles are one of nature’s great protein recyclers. They can fly hundreds of miles a day to find a free dinner. And because they are the masters of reading the intentional movements of other eagles, it is not long before the first bird’s “find” is being honed in on by five more, then 20 more and maybe within minutes, 100 more eagles are bee-lining to that same spot. The bald eagle is not just a major scavenger but an effective bully always prepared to steal food from the lesser neighbor, at least until she / he is satisfied. At that satiation point the food is always turned over to the next bully.

So what has all this ‘natural behavior’ got to do with our bald eagles and the impact of some supplemental feeding? Well everything. First, and lets talk about the southern British Columbia coast because this is the geography and its biological timing that we are specifically dealing with. Up until 1953 Alaska offered a bounty on bald eagles and over 111,000 pairs of bald eagle feet were turned in for payment. It is estimated that 7-10 eagles were likely shot for each one retrieved and the bounty paid, so this would probably account for over 1,000,000 eagles being shot over a 20 year period. An incredible impact!
Some Personal History:

When I started my eagle work in the mid 1950’s we had lots of eagles both wintering and nesting in the southern Gulf Islands of British Columbia. These are the islands separated from the San Juan Islands of Washington State by the twisting. meandering Canada/US border. At that time I had 96 nesting pairs of eagles in the Canadian group of these islands. In aerial surveys of the entire Washington coastline. from the Canadian border south to Seattle. and around all the San Juan Islands (I had to avoid flying too close to some military bases!) in between, I did not find a single active nesting pair of bald eagles. There were still lots of unused nests but no nesting birds that I found. Conclusion: between the Alaska fisherman who largely lived out the winter in these milder coastal Washington villages, and the general North American attitude at that time, the attitude was that all predators were “vermin” and were despised competitors with humans and should be shot. The Washington eagles suffered enormously. Not that Canadians were more “conscientious about our natural resources” — we weren’t. But I suspect the Alaska bounty simply propelled a financial return and a reinforcement of how evil eagles were. Every hunting magazine of the day then showed ads for guns, scopes or ammunition with a hawk, eagle or ground squirrel in the ‘cross-hairs’ to reinforce how bad these creatures were. Predators until the mid-1960’s were evil and competitive and existed to be killed. Like most advertising, be it to support violence, greed or good, the repetition works. The Washingtonites did a fine job by the standard of the day. They literally eliminated the bald eagle, their own National Emblem, from its main coastal habitat.

By the early 1960’s the attitudewas beginning to shift. Many bird species were found to be disappearing. Rachael Carson drew the world’s attention to the link between our pesticide poisoning of the entire continent and the disappearance of song birds and raptors. Our ‘human conscience’ was pricked. Somehow in this picture of devastation, particularly through the story of the disappearance of the spectacular peregrine falcon and the United States National Emblem, the bald eagle, we began to evolve an awareness that predators had an important role to play in our shared world. Predators became not competitors, they became indicator species on how well we were treating the entire world. And we weren’t doing well.

The Eagles Comeback:

During my own personal studies of the 1960’s, I had over 1000 British Columbia bald eagle nests under observation with my aerial, boat and ground surveys, I was also able to assess something that did not seem significant at the time. Because I did my graduate studies at UBC in Vancouver I frequently extended my aerial surveys to include the Fraser Valley and surroundings of the Greater Vancouver region. It was interesting that I could only find in that entire area three nesting pairs of bald eagles. One in Stanley Park in downtown Vancouver, one across the harbor in West Vancouver’s Lighthouse Park and another pair on the Indian Reservation at Dollarton in North Vancouver. I found none in the farmland of the Fraser River Valley. It was accepted. Eagles and people didn’t co-exist.

Today I have over 250 pairs of bald eagles nestingin this same Great Vancouver – Fraser Valley area. These are the nests I have located, and there are probably another 200 pairs I have yet to locate. An incredible difference. An incredible adaptive acceptance by bald eagles of our urban and city environment. How this all happened is both marvelous but so simple. We humans changed our attitudes. We quit shooting eagles. We did little else. We began to actually honor their existence. They responded.

Sure, in later years we have started to try and preserve the few big trees that will support the huge eagle nests but most big trees are already gone. Our eagles are so eager to occupy our city and urban areas they will even nest on human-made structures cellphone towers and the high tension power towers.. The favored hunting perches have become the telephone pole or industrial cranes, and in parks it is often a totem pole, or around the harbours, the boat masts. I have active nests that are only 37 feet above ground level in driveways. In many parks one can count the number of runners, baby strollers, dogs and playing kids in the hundreds per hour that go directly under the nests — not 60 feet away, not 40 feet away — directly under the nest. I recently was criticized for calling Vancouver the Urban Bald Eagle Capital of the World. Juneau, the Capital city of Alaska (the place where all the Alaska eagle bounties were paid from back in the 1950’s. ) — the city’s PR director called to challenge my statement. They think they now have more breeding eagles than Vancouver. What a wonderful turnaround. What an attitude shift. But as much as I love Juneau and Alaska, it’s just not true. Sorry, Juneau — Vancouver holds the record!

The bald eagle when given a chance adapts well to the urban setting. They quickly learn how to hunt the roads, the farmlands and ditches and the beaches. As a scavenger they are particularly adept at living in our “rubbish filled” environment. They pick up road kills. The cities are ripe each morning with dead rats, cats, rabbits and each day brings forth numerous runover squirrels and mallards. In the spring mallards are killed by the thousands – particularly the males who stand guard on roadways while their hens forage in nearby ditches. Cars runover dozens per day in each region of the Fraser Valley.

Of course Greater Vancouver is blessed with productive ocean frontage, it is bisected by the Fraser River delta, an untold number of small ditches each with salmon, muskrats and waterfowl. The big downside for our eagles is that we don’t have enough big trees to support their huge nests. But they try and, as I stated, have moved into artificial structures. I predict that shortly they will be, like the peregrine falcons, nesting on the bridges and buildings. They are slowly taking back that which was theirs. Marvelous.

Well of course some people don’t like “this taking back”. This involves other adjustments. And of course we don’t really understand what all these adjustments will entail. A big adaptable scavenger/predator moving back into an area must have some impact. But what? It is easy to see that the eagles picking up the rats, dead rabbits and squirrels is pretty positive all around. The downside of this is that these carcasses are not available for the urban coyotes and street dogs and rat fodder.. But maybe that is not so negative! So they now share the cities waste.. Picking up dead ducks is also generally a plus. But what about the live ducks and goslings taken? Nobody would deny we have a lot. The government has for years gone out annually and “shaken” Canada goose eggs by the thousand so they will not hatch. Some people still think we have too many geese and ducks, particularly on the golf fairways. It is also interesting that almost every golf course has an eagle’s nest! Of course, the golf courses have the nest trees.

There is another relationship on the horizon that may shift. What is the present great blue heron population or perhaps more importantly, what was it before Europeans exploited this area? There is occasional evidence that eagles can and will predate heron nests. They will eat the young herons. How natural is this and how will this effect the heron populations? Most certainly herons are another incredibly beautiful and abundant species that share our city and urban areas. Not every Koi or goldfish pond owner likes the herons but generally they are a magnificent contribution to our area and the same patchwork of ditches and streamlets that supports eagles, supports herons. I have had both herons and eagles ‘work’ my large fish pond. But guess who I favor?

The conflict between eagles and herons is not clear. As stated we have recorded incidents of eagles taking juvenile herons out of the nests. But the largest heron colony near to Vancouver, with about 200 pairs of herons, have their nests quite tightly concentrated around an active bald eagle’s nest. That pair of eagles does not appear to kill herons. Another startling observation occurred two years ago. The eagle’s nest blew down in a storm and the new eagle nest was located about 150 meters farther west along the ridge of trees supporting the heronry. The herons then repositioned the centre of their heronry around this new eagle nest location, abandoning the heron nests farther east and now farthest from the new eagle nest. Did the herons move to be near the eagle nest? That is certainly the result. Will this repositioning of the heron nests closer to the eagle nest result in more young herons being raised? Or more being eaten? Time, and a present graduate student, may answer that interesting question.

It is my theory that these herons have recognized that this breeding pair of eagles does not bother them but rather, because of the eagles’ territorial defense of their own territory against other passing eagles, becomes the defender of the heron nests. And the herons recognize this. Incredible. This same mechanism works with Siberian Red-breasted Geese. They primarily and most successfully nest near gyr falcon eyries. The gyr drives off encroaching foxes preserving both the gyr eggs and the geese eggs.

So back to feeding bald eagles. Good or bad? Probably a poorly worded question. Is it justified to ever offer food to a wild bald eagle. Most certainly yes. Could it be negative? Probably yes. So like most circumstances of real life we have to evaluate the individual situation. In the perfect world, where no humans were selectively destroying some habitats and creating others, nature would do all the adjusting. Species would survive or die out depending on their adaptive abilities. We impose an incredible unbalanced selective pressure. At times we can show compassion and understanding. At times we can help restore or tip the scale in another direction — another direction to destruction.

Lets look at a few of the traditional yeses or the positive things we can do. In the 1960’s I made a film showing a young chap at Bella Bella, a fishing village up the BC coast feeding bald eagles. Daily Sonny Dickson threw out meat scraps from his cannery butchershop on the dock to the waiting eagles. Now this was probably 1966, barely at the time of our societal shift from considering all predators as vermin to viewing predators being a desired parts of the ecosystem. The prevailing fisherman attitude in these wilderness areas was still “a predator that eats salmon is bad”. It was the likes of Sonny and his totally unplanned efforts, efforts motivated by his interest in watching these birds’ spectacular aerial maneuvers, that were and still are the roots of conservation.

The eagles were not yet protected as Sonny threw out the fish. Daily fisherman gathered to just watch this spectacle. Many a US fisherman passed those docks, stopping for gas and food, going to and from the Alaska ports, but no eagle around Bella Bella would dare be shot. Sonny, single handed had changed the region’s attitude. Finding within each of us something that sparks an interest or concern, that is conservation. The simple act of feeding these birds gave opportunity to pleasure and wonderment. Killing these magnificent predators was no longer the option.

Historically, and that covers 15,000 to 8,000 years ago,at every native village along the coast where it is believed over a million natives lived off the sea, daily the frames, guts and heads of excess salmon, cod or halibut would be thrown or offered back to the sea. The beach or the sea was the garbage dump. Bald eagles from these early times have mutually benefitted from being fed from humans and I can see no negative effects on these eagle populations. The First Nations people honored and revered the bald eagle, their spiritual connection with their ancestors.

From the 1960’s till today I have seen hundreds, perhaps thousands, of fisherman throw out an unwanted ‘course’ species of fish or the scraps and watch as an eagle came to pick up the offering. What a thrill each has experienced. I have heard the story over and over. It is the story of imbedded interest, of initiating a spark of personal involvement, of sewing the seeds of commitment to nature. The diving of the eagle from a nearby tree, the great extended yellow talons reaching out and striking the fish and swish, it is off. These simple little acts, seeing the eagle at close range, marveling at the bird’s aptitude, this is the triggering mechanism for the beginning of appreciation of nature. Are these acts of feeding eagles wrong? Not at all. These are the acts of involvement, commitment and conversion. Have they somehow unwittingly deterred the eagle from maintaining its wild abilities. Obviously not at all. We have had 10,000 years experiment, probably the greatest and longest experiment ever: Does feeding bald eagles make them less adaptive or successful? Obviously not!

Can a government PR person say feeding an eagle is right? From recent comments, apparently not But that does not make it less right or even less desirable to feed the eagles. “Double-speak” speaks! My obligation is to see that “Double-speak” does not inhibit our eagles success.

Concerns of Feeding:

I have promised to talk about the negative side of feeding eagles or other wildlife. Like the above discussion, the published papers or opinions largely come from which side of the “double-speak” argument you come from. But there is at least one serious concern. And a few other concerns that are more theoretical I suspect than real. The often quoted concern that I don’t give much credence to is worrying that eagles might lose their natural instincts to forage. Are we likely to handicap an eagle from competing successfully? Obviously not – the 10,000 year experiment on our coast Native Americans attests to that.

The negative behavior modification of a long-lived highly mobile scavenger/predator like the bald eagle is really quite unlikely quickly changed. They will readily move several hundred miles in a day in pursuit of food. If the fish run of a river lasts 3 months they will likely stay and feed for 3 months. If all the fish are washed away, as happened in 2007-8 winter along our southern BC coast, so that the run is gone in the first month, then the eagles have to go elsewhere. And it appears that many did. Just that.

Did the local garbage dumps offer an alternative. It seems some did. Did some of the eagles move farther away in pursuit of other food sources? It surely seems that many did. One of our CAM observers usually had 3 to 5 eagles visit her reservoir in Kansas each of the past several years. This year 300 eagles showed up. It sure would have been nice to have had some of those eagles wearing satellite transmitters so we knew where they came from?

They performed as eagles have for hundreds of thousands of years. When the food supply dried up, or in this case washed out to sea, they simply extended their search. Would those few eagles that stayed in local human garbage dumps learn a wrong message? Perhaps, but the few that stayed were a small group of the whole population compared to that which left or went elsewhere. It may be that this variant was positive and not negative to the eagle population.

Note: a 2008-09 update:This past fall turned up some very negative observations. Many of the British Columbia southern rivers had record small salmon returns. What happened to these fish is still not certain. Some facts have been turning up. At the Squamish river system, where the Brackendale-Squamish Bald Eagle Festival, the Festival that has had the largest NA counts, this 2008-09 fall had the lowest numbers of eagles in attendance. The Squamish River system had earlier suffered a disastrous train derailment in which many tank cars of poisons were dumped into the rivers killing the salmon and trout. This same 2008-09 fall saw the Chehalis–Harrison River complex, the home of the Fraser Valley Bald Eagle Festival, show record numbers of eagles. We previously had around 1500 show up for our festival or just after it, but this year we counted over 2500 eagles. And yesterday, January 19, 2009, I did my eagle surveys around Boundary Bay and the Delta Refuse Dump and found record numbers of eagles. The dump count was 781 eagles, up considerably from a previous 9 year high of 640 eagles.

These changes can indeed foretell of ominous disasterous losses in our salmon runs that would surely have great negative impact on the NW bald eagle populations. In the short term however, what these changes in numbers point out is that our eagles are adaptable. They can and do move over considerable distances and very quickly to take advantages of local food – a good salmon run or a garbage dump.

Was the garbage dump negative to the eagles future? Possibly the food content of the Vancouver dump was more contaminated than wild food but I personally doubt that. Some other recent evidence, just released this past week (Jan/09), gave evidence that the last couple of years decline in Orcas in southern BC and Washington, has now been attributed to spring salmon losses. More importantly, these salmon are now shown to be heavily loaded with PCM’s and other pesticides. So if the wild salmon are that contaminated can the human waste dumps be much different. I doubt. The ominous forecast from this salmon-Orca story is that if these predators are suffering from the total contamination of the Pacific Ocean, will our bald eagles not be exhibiting the same losses. Most certainly they are eating from the same table.

On the other hand we do know that farm-raised salmon is often reported to be about 4 times more contaminated than wild salmon so the potential contamination from eating human food is not good. On the other hand the wild salmon are all now so contaminated that a steady diet of these carcasses is probably even worse. I personally gave up eating fish from the Pacific Ocean in 1983 when 26 species in California were all described as “too toxic for human consumption” – that was 1983 – and our oceans are only getting worse.

Another item: An interesting law was recently passed in Alaska, yes the same Alaska that 50 years ago was offering a bounty on eagles. They are saying that people will not be allowed to feed eagles or some variant of this. The law was absolutely aimed at the feeding of eagles by one lady, Jean Keen, at Homer, Alaska spit. She has fed the birds for years. She indeed has a following of eagles and eagle supporters.

One neighbor, a retired Fish and Wildlife biologist who has a game farm nearby with open pens of waterfowl, did not like his ducks being caught by the eagles that he believes she attracts.. He got support from some of his cronies and had this law passed so Jean could not attract the eagles — and presumably his ducks will benefit. Well the law backfired. By popular demand they had to put in an exception to the law, that Jean Keen could keep feeding her eagles. The jury of peers thought the law unjust. Of course, the biologists supporting the law that one “shouldn’t feed wildlife”, remember the “double-speak”, well, they managed to leave their law in place and exclude Jean from it. Is that “double-double-speak”? Sometimes the politics of conservation and defending “double-speak” are more difficult to fathom or cope with than just getting people interested and concerned with the existence of the world’s species.

Another possible problem is that the artificial gatherings of wildlife can bring about unnatural opportunities for predation. Or at least one argument is that ‘artificially fed populations” are therefore unnatural. But concentrations of wildlife at waterholes, natural disasters or due to climatic fluctuations are also quite natural. That a coopers hawk or merlin makes a score at a bird feeder can be quite disturbing to some bird feeders but it is a ‘natural response’ by the predator to a high temporal concentration of prey — a very natural response. And the prey learn what to do or the raptor also gets fed picking off the less weary or fit prey.

I have always been astounded by bald eagles. They can be so aggressive in establishing a territory but when 300 pounds of seal washes up on the beach below the nest, this great food source will be gorged on by dozens of resident and transient eagles. Extra food, if temporarily abundant, is regularly shared by passer bys! Why fight over a food supply that will possibly be gone on the next high tide. The conflict of intra-species aggression is the other half of the selection process.
The Big Danger of Wildlife Feeding:

The big danger of wildlife feeding is probably related to a common wildlife/human problem. When one gets crowds one gets easier transmission of disease, be that between people, wildebeests on the Serengeti or eagles at a salmon stream or in the local dump.

The backyard birdfeeder could be a place where disease transmits more readily from one bird to another. Of course many species do naturally congregate in groups so aggregations are not uncommon. Scavengers, like the eagle of course, do have built-in resistance greater than most species to resist disease as their life is spent digging though dead and diseased carcasses. That is their role.

However, a single example of what can go wrong with artificial feeding, is very pertinent. In most areas of the world, and the Fraser Valley is no exception, the main protein food for humans is poultry. All these chickens are raised in huge barns, best thought of as virus incubators — a place in which disease organisms can breed and multiply and test both their lethalness and their transmissibility.. These chicken or pig barns will likely be the source of the impending “avian and pig” viruses that will spread to people and ultimately kill hundreds of millions of people. The question is not “will this happen” but “when will it happen”.

Why on earth do we allow these virus incubatorsin the proximity of people or on the world’s greatest wild bird migratory path, the Fraser Valley Flyway? Insanity and greed. I say it is greed by the farmers and paid off politicians and insanity by us who allow it. The farms regularly dump the manure and dead carcasses onto the nearby fields where the gathering of starling, crows, gulls and eagles feast. Of course if these carcasses are contaminated with a deadly virus from those barns, then these farmers have now spread their disease to the wild flocks, to their neighbors, to you. And we allow it. We are a greedy species and so self destructive and stupid. We deserve the impending pandemic!

I am told the US requires the chicken farmers to decompose all this manure and rotting dead chickens (in some areas) in enclosed decomposing sheds. These are closed so that no wild birds enter and no diseases escape. The heat from the decomposition kills any virus. Why do we in Canada not demand this? I suppose we have to kill a few more hundreds or thousands of people and 100’s of thousands of local flocks of pet and domestic birds before we address this issue properly!! We had the warning three years ago when nearly 300,000 pets and domestic birds in the Fraser Valley were slaughtered to protect this dangerous industry and appease the US government so our chicken farmers could continue to export our chickens to the US. And we have done nothing to exclude these farms from the Fraser Valley.

So how good for eagles is feeding bald eagles. I think it makes up for a small part of their food supply that we have already taken from them.

Red-tailed Hawk Identification(Buteo jamaicensis)

This page offers Red-tailed hawk identification characteristics when viewing both adults and juveniles in the field. Many people can recognize a "Red-tail" when they see the bird's red tail.

Juvenile Red-tailed Hawk Identification from below:

Click on the photo of the flying juvenile (immature) Red-tail Hawk to the left to see the characteristics that identify this bird (picture is of Eastern Race).

Pale panel on outside of upper side of wing - This pale mark is on the primary feathers and the primary coverts. It can also be seen from the underside if light is shining through from above. According to Wheeler and Clark in A Photographic Guide to North American Raptors, this is the best character to identify all juvenile Red-tailed Hawks.

Juvenile Red-tailed Hawk Identification from the back:

Click on the photo of the perched juvenile Red-tail Hawk to the left to see the characteristics that identify this bird from behind.

Pale panel on outside of upper side of wing - This pale mark is on the primary feathers and the primary coverts. It can also be seen from the underside if light is shining through from above.

Notice that the tail is light brown (not red), with narrow bands. Also notice, that the eye (iris) is light (compare to adult below).

Adult Red-tailed Hawk Identification from below:

Click on the photo of the hand-held adult Red-tail Hawk to the left to see the characteristics that identify this bird from below.

Dark Patagial Mark - as with the juvenile picture above, this mark should be visible on all light phase Red-tailed Hawks of all sub-species. Remember to Look for this field character first.

This particular bird also has a faint belly band. This character is not obvious on all adults. Also notice that the red tail can be seen through the tail from below.

Watch the video: Οι Αετοί και τα Γεράκια (November 2022).