Rough-legged Hawk
As winter sets in, with many birds of spring and summer long since departed to the south, Rough-legged Hawks make their annual appearances in various open habitats across the United States, from sagebrush to grassland to coastal marshes. The hawk species with the northernmost breeding range in North America, Rough-legged Hawks breed in the high Arctic, nesting on cliffs and rock outcrops and feeding on small boreal mammals.

Rough-legged Hawks breed in tundra, forest, and forest edges, from the Aleutian Islands across northern Alaska and Canada to Labrador, and across extreme northern Europe and Siberia. They are completely migratory, leaving their breeding grounds in September and wintering throughout most of the United States (except the southeastern states) and parts of southern Canada. Wintering Rough-legged Hawks may also be found in central and eastern Europe through Russia, Kazakhstan, and China to the Korean Peninsula and Japan.
Rough-legged Hawk Range Map

Migrating Rough-legged Hawks are most often seen traveling singly or in small groups; they are relatively uncommon at most established raptor-migration viewing hot spots. In spring, migration by adult Rough-legged Hawks tends to occur at least a month earlier than the migration of first-year individuals. Such linkages between age and the timing of migration are not evident in fall. Three separate sources of data show that female Rough-legged Hawks tend to be more abundant at northern latitudes in winter, and that males tend to predominate in southern areas. The reason for this apparent tendency is not known.

During the breeding season, Rough-legged Hawks eat mostly lemmings and voles, as well as occasional birds. In winter, they feed primarily on voles, mice, and shrews. Rough-legged Hawks often scan for food while gliding or hovering in the air. They also forage from high perches, such as utility poles or trees, especially in winter. Experimental data suggest that Rough-legged Hawks may be able to see vole urine and feces, which reflect ultraviolet light; such visual ability may enable Rough-legged Hawks to identify areas of high vole concentrations even when the prey themselves are hidden.

The nests of Rough-legged Hawks are usually located at the tops of cliffs. Nests are large, rough structures made of sticks and lined with grass, feathers, and fur. Caribou bones are also sometimes used. Males deliver nest material to females, who build the nests.

Clutch sizes range between one and six eggs, generally averaging three to four eggs in most documented locations and years. At least one source suggests that clutch sizes may vary with the abundance of prey, but this correlation has not been quantitatively verified. Females incubate eggs; males provide food to the female on the nest, and on rare occasion, cover the eggs when the incubating female leaves the nest for brief spells. For the first two weeks after hatching, females and sometimes males feed young small bits of food torn from prey; thereafter, young Rough-legged Hawks can swallow lemmings whole.

Rough-legged Hawks are large birds of prey, measuring about 20 inches in length; females are generally larger and almost always heavier than males. Plumage is highly variable. Most individuals are relatively light; from below, light-morph Rough-legged Hawks show mostly white wings with black tips, dusky trailing edges, and dark patches at the “wrist” (bend of the wing). Upperparts are mottled brown, gray, and white, tending toward lighter coloration on the nape and head. Throat is mostly white. Dark-morph Rough-legged Hawks are almost entirely dark brown or nearly black; from below, they show dark underparts and underwing coverts, with mostly white, faintly barred remiges with black tips and black trailing edges. Intermediates between the two morphs are uncommon. In all plumages, Rough-legged Hawks have feathers on their legs. They hold their wings in a shallow dihedral (V shape) in flight.

Unlike most buteos, Rough-legged Hawks show clear sexual dimorphism in plumage, distinguishable especially in light morphs. Females have solidly dark bellies and single dark tail bands, with more distinct wrist-patches; males are lighter overall, with barred bellies and tails with smaller, thinner bands in addition to the broad band at the tip. Juveniles resemble females, with subtle differences in color and barring.


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