Red-tailed hawk

The red-tailed hawk (Buteo jamaicensis) is a bird of prey that breeds throughout most of North America, from the interior of Alaska and northern Canada to as far south as Panama and the West Indies. It is one of the most common members within the genus of Buteo in North America or worldwide. The red-tailed hawk is one of three species colloquially known in the United States as the 'chickenhawk', though it rarely preys on standard-sized chickens. The bird is sometimes also referred to as the red-tail for short, when the meaning is clear in context. Red-tailed hawks can acclimate to all the biomes within their range, occurring on the edges of non-ideal habitats such as dense forests and sandy deserts. The red-tailed hawk occupies a wide range of habitats and altitudes including deserts, grasslands, coniferous and deciduous forests, agricultural fields and urban areas. Its latitudinal limits fall around the tree line in the Arctic and the species is absent from the high Arctic. It is legally protected in Canada, Mexico, and the United States by the Migratory Bird Treaty Act. The 14 recognized subspecies vary in appearance and range, varying most often in color, and in the west of North America, red-tails are particularly often strongly polymorphic, with individuals ranging from almost white to nearly all black. The subspecies Harlan's hawk (B. j. harlani) is sometimes considered a separate species (B. harlani). The red-tailed hawk is one of the largest members of the genus Buteo, typically weighing from 690 to 1,600 g (1.5 to 3.5 lb) and measuring 45–65 cm (18–26 in) in length, with a wingspan from 110–141 cm (3 ft 7 in–4 ft 8 in). This species displays sexual dimorphism in size, with females averaging about 25% heavier than males. The diet of red-tailed hawks is highly variable and reflects their status as opportunistic generalists, but in North America, it is most often a predator of small mammals such as rodents. Prey that is terrestrial and diurnal is preferred so types such as ground squirrels are preferential where they naturally occur. Large numbers of birds and reptiles can occur in the diet in several areas and can even be the primary foods. Meanwhile, amphibians, fish and invertebrates can seem rare in the hawk’s regular diet; however, they are not infrequently taken by immature hawks. Red-tailed hawks may survive on islands absent of native mammals on diets variously including invertebrates such as crabs, or lizards and birds. Like many Buteo, they hunt from a perch most often but can vary their hunting techniques where prey and habitat demand it. Because they are so common and easily trained as capable hunters, the majority of hawks captured for falconry in the United States are red-tails. Falconers are permitted to take only passage hawks (which have left the nest, are on their own, but are less than a year old) so as to not affect the breeding population. Adults, which may be breeding or rearing chicks, may not be taken for falconry purposes and it is illegal to do so. Passage red-tailed hawks are also preferred by falconers because these younger birds have not yet developed the adult behaviors which would make them more difficult to train. 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. 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). 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 of course 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 hues, 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. 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. The cere, the legs, and the feet of the red-tailed hawk are all yellow, as is the hue of bare parts in many accipitrids of different lineages. 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 hue, which is the adult eye-color in all races. 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. Though the markings and hue 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. 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. 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. Red-tailed hawks tend have a relatively short but broad tails and thick, chunky wings. Although often described as long winged, 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 (Buteo lagopus) and 44 g (1.6 oz) per square cm in the red-shouldered hawk (Buteo lineatus). In contrast, the red-tailed hawk weighed considerably more for their wing area: 199 g (7.0 oz) per square cm. As is the case with many raptors, the red-tailed hawk displays sexual dimorphism in size, as females are up to 25% larger than males. As is typical in large raptors, frequently reported mean body mass for Red-tailed Hawks are somewhat higher than expansive research reveals. Part of this weight variation is seasonal fluctuations, hawks tending 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 averaging somewhat longer winged and tailed. Male red-tailed hawks may weigh from 690 to 1,300 g (1.52 to 2.87 lb) and females may weigh between 801 and 1,723 g (1.766 and 3.799 lb) (the lowest figure from a migrating female immature from Goshute Mountains, Nevada, the highest from a wintering female in Wisconsin). 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. The largest known survey of body mass in red-tailed hawks is still credited to Craighead & 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, apparently from natural history collections in Wisconsin and Pennsylvania, without note to the region, age or subspecies of the specimens. 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, average 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). Size variation in body mass reveals that the red-tailed hawks 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. 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. The 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. 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. 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. 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). Other larger adult Buteo in North America usually have obvious distinct markings that are absent in red-tails, whether the rufous-brown “beard” of Swainson's hawks (Buteo 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). In perched individuals, even as silhouettes, the shape of large Buteos may be distinctive, such as the wingtips overhanging the tail in several other species, but not in red-tails. North American Buteos range from the dainty, compact builds of much smaller Buteos, such as broad-winged hawk (Buteo platypterus) to the heavyset, neckless look of ferruginous hawks or the rough-legged buzzard which has a compact, smaller appearance than a red-tail in perched birds due to its small bill, short neck and much shorter tarsus, while the opposite effect occurs in flying rough-legs with their much bigger wing area. In flight, most other large North American Buteo are distinctly longer and slenderer 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 (but not always) also lack the dark subterminal tail-band, and ferruginous have a totally feathered tarsus. 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. More difficult to identify among adult red-tails are its darkest variations, as most species of Buteo in North America also have dark morphs. Western dark morph red-tails (i.e. calurus) adults, however, retain the typical distinctive brick-red tail which other species lack, which may stand out even more against the otherwise all chocolate brown-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 lack. 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 aforementioned). Some darker juveniles are similar enough to other Buteo juveniles that it has been stated that they 'cannot be identified to species with any confidence under various field conditions.' 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 the Harlan’s 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.