It retains much of its original body shape and coloration, but has a hooked beak and pointed wings like a skua. In summer it feeds on rodents and smaller birds in the tundra, but spends its winters in the coniferous forests to the south as a scavenger. Its survival in the cold north is due in no small part to the fact that it is a brood parasite, like with many cuckoos, laying its egg in the nests of other birds to be incubated and hatched by them. In this way it conserves the energy it would otherwise use in nest-building and brood rearing, at the expense, however, of the ducks and waders on whose nests the eggs are laid.