The preferred prey species of the rough-legged hawk are voles and lemmings (2) (3), although as an opportunistic carnivorous predator (3) it will also take small birds, fish, insects and carrion when its preferred prey is scarce (2) (3). It hunts by hovering in the air above open areas (4), as well as from an elevated perch, to which it will return to consume its prey (3) (4). It may also forage around rubbish dumps in certain areas (2).
A migratory species, the rough-legged hawk migrates from its northern breeding grounds between mid-September and early November, and overwinters in the southern areas of its range. Northward migration from the wintering grounds usually occurs between late April and late May (2). Rough-legged hawks usually migrate during the day, and may form large flocks, small groups or fly alone (3).
The male and female rough-legged hawk form a monogamous pair bond for the breeding season, which may be formed during winter before the pair migrates. The pair bond is formed during a courtship ritual which involves calling and flying in circles high in the air. The bond is usually only maintained for one breeding season (3).
Immediately after arrival on the breeding grounds, nest construction begins and usually takes between three and four weeks to complete (3). After the male rough-legged hawk has selected the nest site, it collects most of the nesting material and takes it to the female who constructs the nest (3). The nest itself is usually built on a cliff or rocky outcrop and is a large, bowl-shaped structure built primarily from sticks, with a lining of grass, sedges and twigs (2) (3) (4). As well as sticks, the outer structure of some nests may contain the bones of reindeer (Rangifer terandus) (3) (4). Between May and June (2), a single clutch of between one and seven eggs is laid by the female (4), with the eggs laid at two-day intervals (2). The eggs are highly variable in their appearance and may be green, blue or off-white with blotches and spots on their surface (3) (4). Incubation is performed solely by the female (2) (3), who is fed by the male until the eggs begin to hatch after between 28 and 31 days (3). Between 35 and 45 days after hatching, the young begin to fledge the nest, with males usually fledging the nest around a week before females (2).