The ferruginous hawk (Buteo regalis) is a large bird of prey and belongs to the broad-winged buteo hawks. An old colloquial name is ferrugineous rough-leg, The specific epithet regalis is Latin for 'royal' (from rex, regis, 'king'). The common name 'ferruginous' means 'rust-colored' or 'reddish-brown'.

This species is a large, broad-winged hawk of the open, arid grasslands, prairie and bush steppe country; it is endemic to the interior parts of North America. It is used as a falconry bird in its native ranges.

Description

thumb|left|Dark-morph bird on nest

thumb|left|Light-morph in captivity

This is the largest of the North American Buteos and is often mistaken for an eagle due to its size, proportions, and behavior. Among all the nearly thirty species of Buteo in the world, only the upland buzzard (B. hemilasius) of Asia averages larger in length and wingspan. The weight of the upland buzzard and ferruginous broadly overlaps and which of these two species is the heaviest in the genus is debatable. As with all birds of prey, the female ferruginous hawk is larger than the male, but there is some overlap between small females and large males in the range of measurements. Length in this species ranges from with an average of , wingspan from , with an average of about , and weight from . Weight varies in the species relatively restricted breeding range. In the southern reaches of the species breeding range, i.e. Arizona, New Mexico and Utah, males average , in a sample of fifteen, and females average , in a sample of four. In the northern stretches of the breeding range, in southern Canada, Washington, Idaho and North Dakota, the hawks are heavier averaging in males (from a sample of 30) and in females (from a sample of 37). Upland buzzard average weights were intermediate between those body mass surveys, notably heavier than the first and less heavier than the latter one, particularly the sample of 37 ferruginous hawk females place it as the most massive type of Buteo in northern populations.

Adults have long broad wings and a broad gray, rusty, or white tail. The legs are feathered to the talons, like the rough-legged hawk. There are two color forms:

  • Light morph birds are rusty brown on the upper parts and pale on the head, neck, and underparts with rust on the legs and some rust marking on the underwing. The upper wings are grey. The "ferruginous" name refers to the rusty color of the light-morph birds.
  • Dark-morph birds are dark brown on both upperparts and underparts with light areas on the upper and lower wings.

There are no subspecies.

Voice

The voice is not well-described in literature. Alarm calls consist of kree – a or ke – ah and harsh kaah, kaah calls, the latter resembling some vocalizations of the herring gull. One description referred to the "wavering" alarm call and "breathy" notes, while other authors describe screams similar to those of the red-tailed hawk (B. jamaicensis).

Identification

thumb|right|In flight as seen from below

thumb|Ferruginous Hawk showing wings, tail, and dark legs, near Las Vegas, New Mexico

thumb|Skull of a ferruginous hawk

The male and female have identical markings. The main difference is size, with the female being somewhat larger. Perched birds have a white breast and body with dark legs. The back and wings are a brownish rust color. The head is white with a dark streak extending behind the eye. The wingtips almost reach the tip of the tail.

The underside is primarily light colored with the dark legs forming a "V" shape. The reddish upper-back color extends to the inner wing-coverts or "shoulders." The primary remiges (pinions) are dark gray with conspicuous light "windows" in the inner primaries. Three prominent light areas on the upper surface stand out as two "windows" on the outer wings and a rufous rump mark, perhaps the most significant feature of a flying ferruginous hawk. The underwings are whitish overall with rufous markings, particularly in the patagial area. This gives a smudgy appearance to the wings, but less dark than in a red-tailed hawk. The ferruginous hawk is noticeably longer winged than a red-tailed hawk, although the wings appear slenderer than the latter species the total wing area of the ferruginous is considerably more. However, red-tailed hawks can be nearly as bulky and heavy. Dark "comma"-shaped markings are prominent at the wrists. The ferruginous hawk is one of only two hawks that have feathers that cover their legs down to their toes, like the golden eagle. The other is the rough-legged buzzard (Buteo lagopus). The pale morph of the closely related but more slender rough-legged species is best distinguished by its darker coloration, with a broad black tail band and a dark band across the chest. The dark morph Rough-leg is more a slaty coloration than the more brownish dark morph ferruginous. Swainson's hawks and especially rough-legged buzzards can be nearly as long-winged but are less bulky and heavily built than the ferruginous. Among the normal standard measurements, the wing chord measures , the tarsus measures and the tail measures . Additionally, the grasp is and the third toe , indicating that the ferruginous hawks has the largest and most robust feet of any of the world's Buteos. Compared to other Buteos, the ferruginous has a larger bill, at , with a much wider gap when the bill is opened, at .

  • Perch and Wait – perching is on any elevated natural or man-made site
  • Ground Perching – the hawk will stand on the ground at a rodent burrow after initially locating it from the air. As the burrowing animal reaches the surface, the hawk rises into the air and pounces upon it even while it is still underneath the loose earth.
  • Low-level Flight – birds will course over the landscape within a few yards of the ground and pursue in direct, low-level chases, or they will hunt from above the ground.
  • High-level Flight – birds will hunt while soaring, but the success rate is generally low.
  • Hovering – using quickened wing beats, often in times of increased winds, the birds will search the ground and drop on the prey.
  • Cooperative Hunting – mates have been known to assist each other.
  • Piracy – the ferruginous hawk has been observed gathering around a hunter shooting prairie dogs, and claiming shot "dogs" by flying to them and mantling over them.

In its "strike, kill, and consume" type of predation, the prey is seized with the feet and a series of blows may be meted out, including driving the rear talon into the body to puncture vital organs. Biting with the beak may also take place. Before bringing prey to the nest, the adults will often eat the head. At the nest, birds are plucked and mammals torn into pieces before being fed to the young. Food caching has been noted, but not generally near the nest.

Prey species

The diet varies somewhat geographically, depending upon the distribution of prey species, but where the range of the ferruginous hawk overlaps, rabbits and hares are major food species along with ground squirrels and pocket gophers. In South Dakota, thirteen-lined ground squirrels (Spermophilus tridecemlin) are dominant prey, while northern pocket gophers (Thomomys talpoides) and Great Basin pocket mice (Perognathus parvus) was predominantly taken in Washington. Similarly, Botta's pocket gophers (Thomomys bottae) was important prey in New Mexico along with Gunnison's prairie dogs (Cynomys gunnisoni) and desert cottontails (Sylvilagus audubonii). Black-tailed prairie dogs (Cynomys ludovicianus) were the only prey observed captured by ferruginous hawks during winter in Colorado, where remaining prey was either scavenged or kleptoparasitized. Richardson's ground squirrel (Urocitellus richardsonii) was the dominant prey item in ferruginous hawk diets in southern Alberta and Saskatchewan. In the northwest Texas panhandle, the Oklahoma panhandle, and northeastern New Mexico in 2003–2004, ferruginous hawks primarily delivered plains pocket gophers (Geomys bursarius) and yellow-faced pocket gophers (Cratogeomys castanops). Larger black-tailed jackrabbits (Lepus californicus) is the main prey in Northern Utah and Southern Idaho, comprising 83% of the total biomass. These jackrabbits can weigh around , though young individuals are largely taken along with adults. Similarly, they can even regularly hunt young white-tailed jackrabbits (Lepus townsendii), one of the largest lagomorphs in North America, and adults weighing around can be infrequently taken. In one instant, a pair of ferruginous hawks succeeds at killing a large jackrabbit about in weight. Other lagomorph and rodent prey include various mouse such as eastern deer mice (Peromyscus maniculatus), voles such as montane voles (Microtus montanus), Townsend's ground squirrels (Urocitellus townsendii), western pocket gophers (Thomomys mazama), muskrats (Ondatra zibethicus), eastern cottontails (Sylvilagus floridanus), giant kangaroo rats (Dipodomys ingens), and antelope squirrels (Ammospermophilus). Mammalian prey other than lagomorphs and rodents are uncommon, though they occasionally prey on mustelids, such as stoats (Mustela erminea), long-tailed weasels (Neogale frenata), and black-footed ferrets (Mustela nigripes).

Ferruginous hawks can also take a wide range of birds as prey. The most frequently taken avian species are western meadowlark (Sturnella neglecta) and horned larks (Eremophila alpestris) along with other passerines, and dabbing ducks can be important prey at times. They can occasionally prey on relatively large gamebirds such as common pheasants (Phasianus colchicus), lesser prairie-chickens (Tympanuchus pallidicinctus), sharp-tailed grouse (Tympanuchus phasianellus), and sage grouse (Centrocercus urophasianus). Predation on corvids such as American crows (Corvus brachyrhynchos), common raven (Corvus corax), Chihuahuan ravens (C.cryptoleucus) and raptors such as burrowing owls (Athene cunicularia), American barn owls (Tyto furcata), and other Buteo hawks have been reported. While yellow-bellied racer (Coluber constrictor) and garter snake (Thamnophis sirtalis) was constituted the second most frequent prey item in Washington, other snakes such as western hognose snakes (Heterodon nasicus) and pine snakes (Pituophis melanoleucus) can be taken in other regions. the golden eagle can be a serious threat (in potential territorial or defensive conflicts) and predator of the ferruginous. Although they may be attracted to similar nesting habitat, in a local comparison in northwestern Texas, southwestern Oklahoma and northeastern Arizona, the typical prey taken by Swainson's hawks was quite different, being about half the weight of that of the ferruginous hawk and more focused on insects rather than mammals. However, in the Morley Nelson Snake River Birds of Prey National Conservation Area, the prey taken by red-tailed hawks and ferruginous hawks was almost exactly the same, both in terms of species and body size. The prey species hunted by golden eagles are often similar, but the ferruginous hawk is locally less of lagomorphs where it co-exists with eagles and takes typically smaller prey, such as pocket gophers, which are generally ignored by the eagles. It seems to be quite tolerant of conspecifics from adjacent territories.

Reproduction and life history

Copulation occurs during and after nest building. The egg-laying period varies with latitude, weather, and possibly food supply. In the Canadian parts of the range, laying occurs from the latter part of April through late June, whereas farther south laying occurs from about March 20 through mid May. The earliest recorded clutch was in January in Utah and laying could occur as late as July 3 in Canada. Egg-laying occurs at two-day intervals with incubation starting when the first egg is laid. Incubation is shared by both sexes with each taking approximately the same number of shifts during the 32-day average incubation period. Replacement clutches following failure appears to be rare.

Courtship flights seem to be limited in the accepted sense. Both sexes engage in high, circling flight but literature details are sketchy. Soaring activities may primarily be variations on territorial defense flights as opposed to courtship per se. The "flutter-glide" flight consists of a series of shallow, rapid wing beats interspersed with brief glides and may serve to advertise the territory. The "sky-dance" is stimulated by an intruder and consists of slow flight with deep, labored wing beats with irregular yawing and pitching that may terminate in steep dives. In the "follow-soar" maneuver, the male ferruginous hawk will fly below an intruder and escort it out of the territory.

High perching occurs from prominent places around the nest, particularly early in the breeding cycle. Aggressive actions such as attacking, talon-grasping, and pursuit have been noted by some observers. Copulation begins before construction of the new nest, and increases in frequency until the start of egg laying. The passing of food may occur before the activity. The duration of copulation is from four to 18 seconds.

thumb|left|Ferruginous hawk nesting platform

The ferruginous hawk is one of the most adaptable nesters of the raptors, and will use trees, ledges, rock or dirt outcrops, the ground, haystacks, nest platforms, power poles, and other man-made structures. Within some broad categories such as cliffs, the variety includes clay, dirt and rock substrates. Tree nests are typically in isolated trees or isolated clumps of trees in exposed locations. Authors differ as to whether ground nests are more successful than tree nests, but they are more susceptible to mammalian predation. Nest locations are reused frequently, but several nests may be built in an area. Typically, one or two alternate nests may exist but up to eight have been found on some territories.

The nests are made of ground debris such as sticks, branches, and cattails. Old nests will be refurbished, or nests of other species may be taken over and refurbished with sticks being added on top of the old nests. Odd items such as paper, rubbish, barbed wire, cornstalks, plastic, and steel cable have been incorporated into nests. Bark from trees and shrubs will be used for lining along with grasses and cow dung. Bits and pieces of greenery are often added to the nest. Prior to the removal of the bison from this bird's range, nesting material often included bison bones, fur and dung. Both sexes are involved with building the nests and bringing materials, but the male seems to be more involved in retrieving materials while the female arranges them in the structure.

thumb|left|Chicks on nest

Clutch size varies from one to eight and is likely linked to food supply. The average clutch is three to four eggs, each long and wide. They are smooth, non-glossy and whitish in color, irregularly spotted or speckled and blotched with reddish-brown markings. There may be a concentration of darker pigments at the small end of the egg. Occasionally, the eggs are almost unmarked or have faint scribblings on them.

The nestling period varies from 38 to 50 days with brooding primarily by the female. Males fledge at 38 to 40 days and the females as late as 50 days after hatching, or 10 days later than their male siblings as they take longer to develop. Nestlings lie or sit for the first two weeks, stand at about three weeks and walk soon after. By 16 or 18 days, they are able to feed on their own. Wing flapping starts about day 23 and by day 33 the young are capable of vigorous flapping and "flap jumps." The nestlings are sensitive to high temperatures and seek shade however possible in the nest.

thumb|left|Juvenile

Initial movement out of the nest is felt to be a response to heat stress as the young quickly move towards shade. The initial flight for the males is taken at 38 to 40 days while the slower-developing females fly about 10 days later. Post-fledging dependency upon the parents may last for several weeks. During the first four weeks after fledging, the young patrol increasingly large areas around the nest as they learn to hunt. Young hawks have killed prey as early as four days after fledging.

The ferruginous hawk is single-brooded, and as in so many raptors, the number of young reared is tied closely to food supply. In areas where jackrabbit populations are the principal food source, the initial clutch sizes and the number of reared young vary closely with variations in the number of jackrabbits. Fifty percent loss of young has been reported in low jackrabbit years. Fledging rates of 2.7 to 3.6 young per nest have been reported during years of abundant food supply. The high potential clutch size allows for a quick response to increases in the prey base.

Ferruginous hawks have been known to live for 20 years in the wild, but most birds probably die within the first five years. The oldest banded birds were recovered at age 20. First-year mortality has been estimated at 66% and the adult mortality at 25%. The reasons for mortality include illegal shooting, loss of a satisfactory food supply, harassment, predation, and starvation of nestlings during times of low food supply. Ground nests are susceptible to predation by coyotes, bobcats and mountain lions while nestlings, fledglings and adults may be preyed upon by great horned owls, red-tailed hawks, bald eagles and golden eagles.

Status and conservation

thumb|right|Banding chicks

thumb|upright|Ferruginous hawk at [[Lacreek National Wildlife Refuge]]

At times the ferruginous hawk has been considered threatened, endangered, or of concern on various threatened species lists but recent population increases in local areas, coupled with conservation initiatives, have created some optimism about the bird's future. It was formerly classified as a Near Threatened species by the IUCN, but new research has confirmed that the Ferruginous hawk is common and widespread again. Consequently, it was downlisted to Least Concern status in 2008. For the experienced falconer it offers an opportunity to experience the nearest equivalent to hunting with the golden eagle with much lower risk of injury to the falconer by the hawk. Faster and stronger than the red-tailed hawk, the ferruginous hawk is effective in pursuit of larger hares and jackrabbits that are difficult prey for the red-tailed hawk and Harris's hawk, and with its agility is also more effective on large bird species than is the golden eagle.

References

:Part of this article incorporates text from the Bureau of Land Management, which is in the public domain.

Further reading

  • Ferruginous hawk – Buteo regalis USGS Patuxent Bird Identification InfoCenter
  • Ferruginous hawk Species Account – Cornell Lab of Ornithology
  • ferruginoushawk.org – ferruginoushawk.org
  • Several Closeups of the ferruginous hawk
  • Ferruginous hawk videos on the Internet Bird Collection
  • Ferruginous hawk photo gallery VIREO