Skuas comprise five species of sea birds in the family Stercorariidae, order Charadriiformes. These birds breed on the coastal tundra and barrens of the Arctic and Antarctic, and winter at sea and in coastal waters.
Skuas are gull-like in many respects, with long, pointed wings, short legs, and webbed feet. However, skuas have a strongly hooked beak, elongated central tail feathers, and a generally dark coloration, although some birds are of a lighter-colored phase. Skuas also display a very different behavior from gulls. Skuas are swift, strong, and maneuverable fliers. They are predators of small mammals, eggs and the young of birds and fish, and they also eat carrion when available. Skuas are kleptoparasites—piratical feeders that rob other birds of their prey. For example, skuas may aerially harass gulls until they drop or disgorge fish that they have caught, which is then nimbly retrieved and eaten by the skua.
Although not necessarily common, all five species of skua are widespread in northern regions of both North America and Eurasia. The great skua (Catharacta skua) is a large, brown sea bird that breeds on various islands of the North Atlantic, on Antarctica, and in sub-antarctic regions. The south polar skua (C. maccormicki) is similar in size and shape to the great skua. This species only breeds on Antarctica and on a few sub-antarctic islands such as the South Shetlands, although it wanders widely in the oceans of the Northern Hemisphere during its non-breeding season.
The other three species of skuas are usually called jaegers in North America. All three species have Holarctic distributions, meaning that they breed in northern regions of both Eurasia and North America. The pomarine jaeger (Stercorarius pomarinus) is the most robust of the jaegers, while the parasitic jaeger (S. parasiticus) is somewhat smaller and more widespread. The long-tailed jaeger (S. longicaudus) is the smallest and least uncommon species, breeding as far north as the limit of land on Ellesmere Island and Greenland.