Arctic skua

Here are some facts about the arctic skua (Stercorarius parasiticus), a predatory seabird that is often seen a long way from the Arctic

Distribution and habitat

There are several species of skua, which are typified by being quite large seabirds that spend most of their lives out at sea, and are generally aggressive towards other birds whose food they seek to steal. In the United Kingdom most skuas are seen only in remote areas during the breeding season.

 Despite their name, arctic skuas spend much of the year far from the Arctic, migrating in large flocks to West Africa or the South Atlantic during the northern winter and only returning to their breeding grounds in northern Europe in April or May. In the UK, these grounds are in the northernmost part of Scotland and the northern and western isles, all of which are typified by tundra-like vegetation and a sparse human population.

 Appearance and behaviour

The arctic skua is around 66 centimetres (26 inches) long. It is unusual in that the plumage can vary greatly between individual birds, as well as at different ages and times of the year. "Dark" adults are mostly dark brown with some greyer feathers on the underparts and yellowish streaks on the head and neck in summer. "Light" adults have whitish underparts and are darker on top, with a more speckled underbody in winter. However, there are many variants on the theme, which can make the bird difficult to identify.

 One common feature is the pointed, tapering tail feathers which project up to 10 centimetres in adults but are blunter and shorter in juveniles. The wingtips, which are pointed, are generally paler than the rest of the wing, whatever the colour of the rest of the bird.

 Arctic skuas have quite a varied diet, including fish, invertebrates, berries, washed-up carrion, and the eggs of other species. They will kill and eat small birds and chase after larger birds such as terns and guillemots to make them drop their catch, either flying low across the surface of the sea or twisting in the air to harry the target bird from all directions.

 It has a harsh call that can be heard on the audio recording on this page of the RSPB (RoyalSociety for the Protection of Birds) website.

Breeding

Although arctic skuas are colonial, their nests are well spaced-out, comprising unlined hollows in the grass. The usual clutch is two eggs, which are incubated by both parents in turn, hatching after around 25 days. Both parents also feed the chicks, which fledge at around 32 days, when the migration south usually begins.

A red-listed bird

Arctic skuas are best observed from northern cliff-tops, particularly near tern colonies. During the breeding season it is unwise to approach their nests, as they are particularly aggressive at this time. With only around 2,000 pairs recorded as breeding in the UK, the arctic skua is on the "red list" of threatened species maintained by the RSPB.

© John Welford