This species breeds in the north of Eurasia and North America, with significant populations as far south as northern Scotland. It nests on dry tundra, higher fells and islands, laying up to four olive-brown eggs. It is usually silent except for mewing and wailing notes while on the breeding grounds. Like other skuas, it will fly at the head of a human or fox approaching its nest. Although it cannot inflict serious damage, it is a frightening and painful experience. It is a migrant, wintering at sea in the tropics and southern oceans.
This bird will feed on rodents, small birds and insects but also robs gulls and terns of their catches. Like the larger skua species, it continues this piratical behaviour throughout the year, showing great agility as it harasses its victims.
Identification is complicated by similarities to long-tailed jaeger and pomarine skua, and the existence of three colour morphs. Small for a skua, the parasitic jaeger measures 41–48 cm (16–19 in) in length, 107–125 cm (42–49 in) in wingspan and weighs 300–650 g (0.66–1.43 lb). The tail streamer of the breeding adult accounts for about 7 cm (2.8 in) of their length. Light-morph adults have a brown back, mainly white underparts and dark primary wing feathers with a white "flash". The head and neck are yellowish-white with a black cap and there is a pointed central tail projection. Dark-morph adults are dark brown, and intermediate-phase birds are dark with somewhat paler underparts, head and neck. All morphs have the white wing flash.
Juveniles are even more problematic, and are difficult to separate from long-tailed jaegers. They are bulkier, shorter-winged, and less tern-like than that species, but show the same wide range of plumage variation. The flight is more falcon-like. However, they are usually warmer toned than Long-tailed, with browner shades, rather than grey.
The call of these birds which is most often heard is a nasal mewing sound, repeated a few times in display, whereas its alarm call is a shorter sound.
- BirdLife International (2012). "Stercorarius parasiticus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
-  (2011).
- CRC Handbook of Avian Body Masses by John B. Dunning Jr. (Editor). CRC Press (1992), ISBN 978-0-8493-4258-5.
- Harrison, Peter (1996). Seabirds of the World. Princeton: Princeton University Press. ISBN 0-691-01551-1.
- Bull, John; Farrand, Jr., John (April 1984). The Audubon Society Field Guide to North American Birds, Eastern Region. New York: Alfred A. Knopf. ISBN 0-394-41405-5.
- (Parasitic jaeger = ) Arctic skua - Species text in The Atlas of Southern African Birds
- More Arctic skua information and photos at the Handa Island Skua Project
- RSPB A to Z of UK Birds
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