Rough-legged hawk, Buteo lagopus.

Rough-legged Hawk, Buteo lagopus

Rough-legged hawks are large birds of prey, averaging 48–60 cm in length – the size of a very large crow – and having wingspans of up to a metre and a half. There are two colour forms of this hawk – light and dark – but most rough-legs have a dark band across the chest, white underwings with black patches on the underside of their wrists, and a white patch at the base of their tail. Unlike most hawks, the legs of this species are feathered to the toes – an adaptation to the arctic cold. Rough-legged hawks are circumpolar, migratory birds, breeding throughout the tundra from the treeline north to the central Arctic islands, and wintering in southern Canada and the United States.

Rough-legged hawks usually place their nests on rocky outcrops or cliff ledges protected by overhangs, but they occasionally nest in stunted trees on the edge of the tundra. Nests are constructed of small twigs and other vegetation, and gradually become larger as pairs return to the same nest, adding material each year. On average, these birds lay three or four eggs, but in years of high prey availability, they may lay up to seven. Both the male and female birds participate in incubating the eggs and raising the offspring, but the male does most of the hunting while the female spends more time at the nest.

The reproductive success of rough-legged hawks is closely tied to their diet, which consists of small mammals such as voles and lemmings. In years with large rodent populations, these hawks can raise as many as seven young, but if food is scarce the parents are unable to provide enough food for the growing chicks. In such times of scarcity, the youngest or smallest chicks starve, and may serve as food for their stronger siblings. The mother feeds the young directly for about two weeks, after which time the parent birds simply place dead prey in the nest, leaving the chicks to grab pieces of food. Many young die during this transition period- if food is in short supply, the older, larger, and more aggressive offspring obtain most of the food and may even kill their weaker siblings.