Ferruginous Hawk

Identification

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 51 to 71 cm (20 to 28 in) with an average of 58 cm (23 in), wingspan from 122 to 158 cm (4 ft 0 in to 5 ft 2 in), with an average of about 139 cm (4 ft 7 in), and weight from 907 to 2,268 g (32.0 to 80.0 oz). 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 1,050 g (37 oz), in a sample of fifteen, and females average 1,231 g (43.4 oz), 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 1,163 g (41.0 oz) in males (from a sample of 30) and 1,776 g (62.6 oz) 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.<p>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:<p>There are no subspecies.<p>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).<p>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.<p>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, the Red-tail can be nearly as bulky and heavy. Dark "comma"-shaped markings are prominent at the wrists. The ferruginous hawk is one of the 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 415 to 477 mm (16.3 to 18.8 in), the tarsus measures 81 to 92 mm (3.2 to 3.6 in) and the tail measures 224 to 252 mm (8.8 to 9.9 in). Additionally, the grasp is 94 to 125 mm (3.7 to 4.9 in) and the third toe 29.5 to 45 mm (1.16 to 1.77 in), 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 37.6 to 49.5 mm (1.48 to 1.95 in), with a much wider gap when the bill is opened, at 42.7 to 57 mm (1.68 to 2.24 in).<p>In-flight, these birds soar with their wings in a dihedral.

Taxonomy

Genus: Buteo; Family: Accipitridae; Order: Accipitriformes.

Scientific name

Buteo regalis

Authority

(Gray, GR, 1844)

Order

Accipitriformes

Family

Accipitridae

Genus

Buteo

Range and habitat

The preferred habitat for ferruginous hawks are the arid and semiarid grassland regions of North America. The countryside is open, level, or rolling prairies; foothills or middle elevation plateaus largely devoid of trees; and cultivated shelterbelts or riparian corridors. Rock outcrops, shallow canyons, and gullies may characterize some habitats. These hawks avoid high elevations, forest interiors, narrow canyons, and cliff areas.<p>During the breeding season, the preference is for grasslands, sagebrush, and other arid shrub country. Nesting occurs in the open areas or in trees including cottonwoods, willows, and swamp oaks along waterways. Cultivated fields and modified grasslands are avoided during the breeding period. The density of ferruginous hawks in grasslands declines in an inverse relationship to the degree of cultivation of the grasslands. However, high densities have been reported in areas where nearly 80% of the grassland was under cultivation.<p>The winter habitat is similar to that used during the summer. However, cultivated areas are not necessarily avoided, particularly when the crops are not plowed under after harvest. The standing stubble provides habitat for the small-mammal prey base needed by ferruginous and other hawks. One requisite of the habitat is perches such as poles, lone trees, fence posts, hills, rocky outcrops or large boulders. Ferruginous hawks nest in trees if they are available, including riparian strips, but the presence of water does not appear to be critical to them.<p>The ferruginous hawk maintains minimum distances from other nesting raptors but will nest closer when necessary, suggesting that the distance is not fixed. The "nearest neighbor" distance has varied from less than 1.6 km (1 mi) to as much as 6.4 km (4 mi) with an average of 3.2 km (2 mi). Nests facing different hunting territories are tolerated much closer than nests facing the same hunting territory. The minimum distance between nests is probably about one half mile on densely occupied areas. Nesting densities in several studies have varied from one pair per 10 to 6,345 km2 (4 to 2,450 sq mi). In Alberta, on one study site, there was a stable density of one pair per 10 km2 (4 sq mi), on average with little deviation from this mean. In Idaho, the average home range for four pairs of ferruginous hawk in the Snake River area was slightly over 5.2 km2 (2 sq mi).

Breeding range

NA : sc Canada to wc USA

Non-breeding range

n Mexico

Migration

Complete migrants

Behavior

Migration pattern: Complete migrants.

Conservation

Population trend: rising.

Population trend

rising