Skua

Theskuas/ˈskjuːə/are a group of predatoryseabirdswith seven species forming thegenusStercorarius, the only genus in thefamilyStercorariidae. The three smaller skuas, theArctic skua, thelong-tailed skua, and thepomarine skua, are calledjaegersinNorth American English.
The English word "skua" comes from theFaroesename for thegreat skua,skúgvur[ˈskɪkvʊɹ], with the island ofSkúvoyrenowned for its colony of that bird. The general Faroese term for skuas iskjógvi[ˈtʃɛkvɪ]. The word "jaeger" orJägeris German for "hunter".The genus nameStercorariusisLatinand means "of dung";the food disgorged by other birds when pursued by skuas was once thought to be excrement.
Skuas nest on the ground intemperate,Antarctic, andArctic regions, and are long-distancemigrants. They have even been sighted at theSouth Pole.
Outside the breeding season, skuas take fish,offal, andcarrion. Many practicekleptoparasitism, which comprises up to 95% of the feeding methods of wintering skuas, by chasing gulls, terns and other seabirds to steal their catches, regardless of the size of the species attacked (up to three times heavier than the attacking skua). Larger species, such as thegreat skua, regularly kill and eat adult seabirds, such aspuffinsandgullsand have been observed killing birds as large as agrey heron.On the breeding grounds, the three, more slender northern breeding species commonly eatlemmings. Those species that breed in the southern oceans largely feed on fish that can be caught near their colonies. The eggs and chicks of other seabirds, primarilypenguins, are an important food source for most skua species during the nesting season.
In the southern oceans andAntarcticaregion, some skua species (especially thesouth polar skua) will readily scavenge carcasses at breeding colonies of bothpenguinsandpinnipeds.  Skuas will also kill live penguin chicks and sick or injured adult penguins. In these areas, the skuas will often forfeit their catches to the considerably larger and very aggressivegiant petrels. Skuas have also been observed to directly pilfermilkfrom theelephant seal's teats.
Skuas are medium to largebirds, typically with grey or brown plumage, often with white markings on the wings.The skuas range in size from thelong-tailed skua,Stercorarius longicauda, at 310 grams (0.68 pounds), to thebrown skua,Stercorarius antarcticus, at 1.63 kg (3.6 lb). On average, a skua is about 56 cm (22 in) long, and 121 cm (48 in) across the wings. They have longish bills with a hooked tip, and webbed feet with sharp claws. They look like large dark gulls, but have a fleshycereabove the upper mandible.
The skuas are strong, acrobatic fliers. They are generally aggressive in disposition. Potential predators approaching their nests will be quickly attacked by the parent birds, which usually target the heads of intruders – a practice known as 'divebombing'.
ThegenusStercorariuswas introduced by the French zoologistMathurin Jacques Brissonin 1760 with theparasitic jaeger(Stercorarius parasiticus) as thetype species.
Skuas are related togulls,waders,auks, andskimmers. In the three smaller species, all nesting exclusively in theHolarctic, breeding adults have the two central tail feathers obviously elongated, and at least some adults have white on the underparts and pale yellow on the neck. These characteristics are not shared by the larger species, all native to the Southern Hemisphere except for the great skua. Therefore, the skuas are often split into two genera, with only the smaller species retained inStercorarius, and the large species placed inCatharacta. However, based ongenetics, behavior, andfeather lice, the overall relationship among the species is best expressed by placing all in a single genus.The pomarine and great skuas'mitochondrial DNA(inherited from the mother) is in fact more closely related to each other than it is to either Arctic or long-tailed skuas, or to the Southern Hemisphere species.Thus,hybridizationmust have played a considerable role in the evolution of the diversity of Northern Hemisphere skuas.
The genus contains seven species: