The arctic skua resembles a stocky gull in body form, but it is a bit more steam-lined and predatory looking in its overall appearance.
The arctic skua resembles a stocky gull in body form, but it is a bit more steam-lined and predatory looking in its overall appearance. The species occurs in two colour phases, a light and a dark, as well as intermediates forms. The dark morph dominates in the southern parts of its range, whereas the light morph predominates in northern regions.
Adult birds are approximately 46 cm in length (including the seven to eight centimetre long projected central tail-feathers). The arctic skua weighs 350–600 g. The sexes are similar in appearance.
The summer plumage has a light brown-black cap, grey-brown back and white under-parts. The cheeks are yellowish and the throat is white. A more or less distinct dark band extends across the breast (though this can be absent). The wings and tail are brown-black, and the tail has characteristic pointed, central tail-feathers. The bill and legs are black. The dark phase has a predominantly dark brown plumage, often with a well defined darker cap. In winter plumage of the light phase birds is more speckled and mottled with yellow-brown and white.
The juveniles have variable colouring, but also a distinct light and dark phase. The light phase is a warm brown with a yellow-brown or red-brown tinge. The head and neck are barred and there is mottling across the belly. Juveniles of the dark phase are a chocolate-brown with a darker head and neck, with less mottling than birds of the lighter phase.
Many birds have intermediate colouration between the two extremes. The adult plumage is attained after three or four years. The young can be distinguished from the pomarine skua by darker lines on the head and neck, a thinner bill, less barring across the inside of the wings and relatively dark tail-coverts. The arctic skua also lacks bars on the upper side of the wing and has a slighter build.
The call is a plaintive wailing.
The arctic skua has a circumpolar distribution and occurs both in the arctic and boreal zones. It breeds along the coast and on the tundra in the north Pacific and north Atlantic regions. In the eastern Atlantic it breeds in Iceland, the Faeroes, northern Scotland, along the Norwegian coast, in Svalbard and along the Russian coast, including the islands in the Barents Sea.
In Svalbard, the arctic skua breeds in single pairs on the tundra along the coast over most of the archipelago, but it is rare in the north-eastern parts of the archipelago. The arctic skua arrives at the breeding area in early June, and leaves the archipelago in August-September.
Outside the breeding season they are pelagic and are thought to spend the winter off the coast of south-western Africa.
In the breeding season the arctic skua occurs mainly along the coast, though in some places it can be found inland. The species often occurs in association with seabird colonies, where it obtains food by pursuing other birds and stealing their catch. Outside the breeding season arctic skuas inhabit coastlines and the open sea. This species uses two foraging strategies, depending on its breeding habitat.
In inland areas and in some coastal localities it is predatory eating eggs and chicks of other birds; in other parts of its range small rodents are also important. In coastal colonies it is kleptoparasitic, stealing food from arctic terns, kittiwake and auks, especially Brünnich’s guillemots.
The arctic skua attacks passing seabirds, pursuing them at great speed. The attacked bird disgorges or drops its prey which the skua snaps from the air. Skuas (and several other species inhabiting the tundra) act injured if the nest area is intruded upon, dragging the wings along the ground. They also attack intruders by diving at them, often striking with the feet, bill or wings.
Life history and reproduction
The arctic skua nests in pairs and shows strong nest site fidelity (occupying the same territory year after year). The nest is placed on dry ground, often on a mound with good views of the sea. The nest itself consists of a shallow depression lined with plant material.
The one or two dark olive-brown eggs have dark coloured speckles. Incubation takes about 26 days and is undertaken by both sexes. Most pairs lay their eggs in the first part of July.
Similar to ground-nesting gulls, the young leave the nest soon after hatching. The family remains together with both parents feeding and protecting the young until they are fledged at about five weeks of age.
Management status and monitoring
The arctic skua is probably the most abundant skua in the world. The breeding population in Svalbard is probably about 1000 pairs. The population trend in Svalbard is not known.
The European breeding population is relatively small, with approximately 140,000 pairs and regarded as stable.