ferruginous rough-leg, buse rouileuse, aquililla patas asperas
The ferruginous hawk (Buteo regalis) is a member of the hawk family (Family Accipitridae). “Ferruginous” refers to the rust colored feathers of the light color morph. It is a broad-winged, broad-tailed hawk. Coloration of male and female adults is identical. There are two color morphs, with intermediates. The most common is the light morph. The light morph has a rust or rufous colored back, shoulders, and legs; the head is mostly white with a dark streak extending behind the eye; underparts mostly white; and tail either light gray or white. Rufous colored legs make a contrasting V on light underparts during flight. The less common dark morph has a dark brown to cinnamon head, body, and wings; a whitish tail; and a light area near the wingtips. Immatures resemble light morph adults, but with few or no rust colored markings.
The ferruginous hawk is one of only three species of American hawks (rough-legged hawk and golden eagle) that have leg feathers extending to the talons. The ferruginous hawk’s call is a scratchy kree-a. Its flight is active, with slow wing beats. It also glides with its wings held in either a strong or modified V (dihedral), or flat. Hovering and low cruising over the ground also are used while hunting. The ferruginous hawk is the largest buteo in North America. Length measurements range from 20 to 26 inches, with an average of 23 inches; wingspans range from 48 to 60 inches, with an average of 56 inches; and weights range from 2.2 to 4.5 pounds.
Ferruginous hawks are primarily birds of the Great Basin and Great Plains. The breeding range extends from eastern Washington to southern Alberta and southern Saskatchewan, south to eastern Oregon, Nevada, northern and southeastern Arizona, northern New Mexico, northwest Texas, western Nebraska, western Kansas, and western Oklahoma. The winter range extends across the southwest to Baja California and central Mexico. Occasional sightings may occur in the Southeast during migration.
Ferruginous hawks are birds of open country. Typical habitat 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.
During the breeding season, the habitat preference is for grasslands, sage, 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 a direct, inverse relationship to the degree of cultivation of the grasslands. However, high densities have been reported in areas where nearly 80 percent of the grassland was under cultivation. The winter habitat is similar to that used during the summer.
Ferruginous hawks feed primarily on small to medium-sized mammals, including jackrabbits, ground squirrels, and prairie dogs. They also eat snakes and large insects on occasion. The birds tend to hunt in early morning or late afternoon. Birds typically hunt in four fashions: short distance strikes on prey from the ground, aerial hunting from low altitudes, aerial strikes from high altitudes (300 feet), and flying after prey from a perch. Hunting from the ground appears to be the most successful of the four methods. Since these birds inhabit open country, they can stand by a burrow and wait for prey to appear. Prey is swallowed whole or torn into chunks. The ferruginous hawk then regurgitates a pellet of fur, feathers, bone, and other non-digestible material.
LIFE HISTORY AND ECOLOGY:
Ferruginous hawks construct a bulky stick nest three feet across and two feet tall, in an isolated tree or within a small grove of trees. Before the elimination of bison from much of the West, ferruginous hawks used not only sticks but also bison bones to build nests, and bison wool and manure to line the nests. Nests can also be placed on other elevated sites such as large shrubs, rock outcrops, buttes, haystacks, transmission towers, power poles, and low cliffs. Ground nests also may be constructed. The same nest can be used year after year, with the birds adding more sticks each year. Some nests can reach 12 to 15 feet tall. One or two alternate nests also may exist. Nests are located adjacent to open areas such as grasslands or shrub lands.
Nesting typically occurs from late March through June. Ferruginous hawks lay a single clutch of one to eight eggs per year, with three to four eggs being average. The eggs are whitish in color, with a few irregular reddish-brown specks or splotches. Eggs are approximately 2 ½ inches long and 2 inches wide. Incubation lasts twenty-eight to thirty-two days. The young are born helpless and covered with down. Young are fledged at thirty-eight to fifty days old. The smaller males may leave the nest ten days earlier than their female siblings.
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. Ferruginous hawks have been known to live up to twenty years in the wild, though most probably die within the first five years. Populations of ferruginous hawks seem to have declined in most areas over their range. The ferruginous hawk is listed as a Threatened Species in several states, and is a Federal Species of Concern.
National Geographic Society. 1999. Field guide to the birds of North America, third edition. National Geographic Society, Washington, D.C. 480 pp.
Peterson, R.T. 1980. A field guide to the birds of eastern and central North America, fourth edition. Houghton Mifflin Company, Boston, Massachusetts. 384 pp.
Chris Cook, Wildlife Biologist, Alabama Division of Wildlife and Freshwater Fisheries