The rough-legged hawk (Buteo lagopus), is found in Arctic and Subarctic regions of North America and Eurasia during the breeding season. They winter across southern Canada and the United States in open country, including prairies, fields and marshes.
The name “rough-legged” hawk refers to the legs, which are feathered all the way to the toes. This fairly large hawk is 18- to 24-inches long, with a wingspan ranging from 47- to 55-inches. They weigh from 1.3 to 3.6 pounds and may gain weight in winter. It is the only member of its diverse genus that has a complete circumpolar distribution.
These are dark-brown hawks with lighter colored head and neck. Tails are dark at the tip and pale at the base. Like many hawks they occur in light and dark morphs. Light morphs have pale underwings with dark patches at the bend of the wing. Dark morphs are mostly dark brown but usually show pale trailing edges to the underwing. The wing tips are long enough to reach or extend past the tail when the animal is perched. The rough-legged hawk’s talons and beak are small for their size, reflecting their preferred choice of prey. The red-tailed hawk is chunkier-looking and has a darker head, broader, shorter wings, barring on the wings and the tail, dark leading edge to the wings (rather than the black wrist patch) and has no white base to the tail. The ferruginous hawk is larger, with a bigger beak, a whitish comma at the wrist and all-pale tail.
Rough-legged hawks breed in open country of the arctic. Nests are built with twigs, sedges and old feathers on cliff ledges and rocky outcroppings. They may allow other species including gyrfalcons, peregrine falcons, and ravens to share their nesting cliffs, but they keep other rough-legged hawks away. The female typically lays three to five pale greenish or blue eggs, blotched or streaked with brown, about 2.2-inches long. Minimum incubation period is 31 days, provided almost exclusively by the female, while the male feeds her.
When hunting, rough-legged hawks often face into the wind and hover, scanning the ground below for small mammal prey. It is the only hawk of its size (other than the very different-looking osprey) to regularly hover over one spot, by beating its wings quickly.
Rough-legged hawks eat mostly small rodents such as lemmings and voles, along with some medium-sized mammals and birds. They may be able to see vole scent marks which are only visible in the ultraviolet range, allowing them to cue in on prey. In winter they hunt from elevated perches such as utility poles, trees, fence posts, and haystacks. They will feed on carrion or occasionally steal from other hawks and ravens. Nonbreeding adults eat about a quarter-pound of food daily, a tenth of their body mass. Despite a strong affinity for rodents, rough-legged hawks were once killed as a perceived threat to poultry.
Rough-legged hawks are monogamous for at least the duration of the breeding season, and pairs have been reported staying together on wintering grounds. Adult rough-legged hawks will vocalize alarm calls when intruders approach a nesting site. Fledglings utter begging calls while waiting for their parents to deliver food.
Threats faced by young rough-legs can include starvation when prey is scarce, freezing when temperatures are particularly harsh during brooding, and predation at the nest. Rough-legged hawks, that survive the two years needed to reach adulthood, can live 19 years in the wild, and longer in a zoo. Older birds can be killed by collisions with power lines, buildings and vehicles; incidental ingestion of poison, lead from prey, or illegal shooting.