Rough-legged Hawks are birds of the Alaskan and northern Canadian Arctic, nesting on cliffs or rarely on the ground, but are mostly seen by birders during migration and winter when they visit the Lower 48. They are more common in the northern states, and rare in the southern, concentrating on the Great Plains and in agricultural valleys of the West. Like other Arctic predators, Rough-legged Hawks are somewhat cyclic in breeding success, tied to prey populations. During years of prey abundance, high numbers are noted at subsequent fall and spring hawk watches. Some birds remain north of the US-Canada border region in winter, especially in the East. Rough-leggeds are the only regularly occurring dark-morph buteo across much of the East.
Often found suspended in mid-air hovering or kiting over agricultural areas or grasslands, Rough-leggeds search for mice and voles to pounce on with a quick pull-in of the wings and drop from the sky. When hovering or kiting, they face into the wind to stay aloft as the head stays completely fixed, as if possessing a built-in gyroscope, while the body and tail adjust with the wind, flawlessly adjusting between kiting and hovering with the change in wind. Rough-legged Hawks perch on roadside utility poles, fence posts, trees, or even on the ground as well, in search of prey. When perching in trees, they sit on the smallest twigs at the very top of trees, appearing too heavy for such frail branches.
Rough-legged Hawks are large buteos. Females are larger than males, with the largest birds weighing as much as large Ferruginous Hawks. But unlike other large buteos, they appear delicate, with small feet and a small bill, an adaptation that helps keep their bare parts less vulnerable to cold weather exposure. Rough-leggeds sometimes roost in large groups in winter, often with Ferruginous and Red-tailed Hawks in certain areas. Their call is a descending, whistled scream, similar to Ferruginous Hawk but higher in pitch.
Perched, they are bulky, but small bill is evident. Wing tips nearly reach tail tip. They often sit at a slight angle when in trees, as opposed to upright on utility poles.
In flight, wings are long and somewhat narrow, lacking any bulge, and tail is somewhat long. Silhouette resembles a cross between Red-tailed Hawk and Northern Harrier.
Buoyant and languid in flight, able to gain lift with ease. Relies on powered flight when needed, thus somewhat harrier-like in manner, but able to hover and kite for hours.
Soars with a dihedral and teeters slightly, but not "wobbly" like Harrier.
When gliding, hold their wings in modified dihedral, rarely drooped or flat-winged.
Wing beats are "floppy" similar to harrier, but stiffer and more powerful.
Two age classes, adult and juvenile. Light-morph can be told by unique black belly and wrists, and white-based tail; dark-morph can be challenging. Eyes of juvenile are pale yellow to yellow-brown turning dark brown as adults.
Adult female light-morph is whitish with blackish bellies and wrists, and white tail with defined blackish distal. Show defined dark trailing edge to wings. Adult female brown on top with grayish-white head.
Adult male light-morph varies from white underneath with dark mottling throughout the body and underwings to white underneath with dark bib on upper chest and faint wrist spots. Male tends to be grayer above than female and show multiple black tail bands. Overlap occurs in sexes, some birds not safely assigned.
Juvenile light-morph similar to adult female but with smudgy tail tip, pale windows in outer primaries, and a diffuse trailing edge to wings.
Adult dark-morph dark brown below with slightly darker wrist patches and belly. Adult female can show dark tail with broad, black tip, or have multiple, crooked, white bands, but all dark-morphs lack white base to tail. Adult male dark-morph can be uniformly jet-black underneath, or brownish like female. Blackish males show dark gray-blue cast to upperside, and neatly banded tails. Some adults (especially males) show small white patch on back of the head.
Juvenile dark-morph similar to adult female, but slightly paler overall with dusky trailing edge to wings, and a faint dark tail tip. Upperside shows pale primary windows, and grayish-brown tail with very faint, gray bands. Juvenile dark-morph has slightly paler eyebrow and cheeks than adult, female in their first adult plumage may share this head pattern.
Medium to long distance migrant, moving north in spring from February to May, and south in fall from mid-September through December. Fall migration appears slightly earlier in the West.
In spring, Brockway Mountain, MI, Derby Hill, NY, Braddock Bay, NY, and along the southern shore of Lake Superior are good sites to see Rough-legged Hawks. Gunsight Mountain, AK, sees up to 40% dark-morph in spring; an unusually high percentage. Whitefish Point, MI sees highest total with 526 in a day, and 2,600 in a season.
In fall, Hawk Ridge, MN, and sites along the northern shoreline of the Great Lakes, such as Hawk Cliff, Ontario, see high numbers annually.
Large concentrations on migration do not occur in western U.S., but winter populations in the West are substantial in many areas.
(Map from Cornell Lab of Ornithology's All About Birds. For dynamic distribution maps, visit the eBird website.)