Arctic Jaeger

The parasitic jaeger (North America) or Arctic skua (Europe) (''Stercorarius parasiticus''), is a seabird in the skua family Stercorariidae. It is a migratory species breeding in Northern Scandinavia, Scotland, Iceland, Greenland, Northern Canada, Alaska, and Siberia and winters across the southern hemisphere. Kleptoparasitism is a major source of food for this species during migration and winter, and is where the name is derived from.

Taxonomy

The parasitic jaeger was formally described in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his ''Systema Naturae'' under the binomial name ''Larus parasiticus''. Linnaeus specified the type locality as "within the Tropic of Cancer of Europe, America and Asia" but this is now restricted to the Swedish coastline. The parasitic jaeger is now placed with the six other skuas in the genus '' Stercorarius'' that was introduced in 1760 by the French zoologist Mathurin Jacques Brisson. The species is considered to be monotypic: no subspecies are recognised. The genus name ''Stercorarius'' is Latin and means "of dung"; the food disgorged by other birds when pursued by skuas was once thought to be excrement. The specific ''parasiticus'' is from Latin and means "parasitic". The word "jaeger" is the German word ''Jäger'', meaning "hunter". The English "skua" comes from the Faroese name ''skúgvur'' for the great skua, with the island of Skúvoy known for its colony of that bird. The general Faroese term for skuas is ''kjógvi'' .

Description

Identification is complicated by similarities to long-tailed jaeger and pomarine jaeger, and the existence of three colour morphs. Small for a skua, the parasitic jaeger measures in length, in wingspan and weighs . The tail streamer of the breeding adult accounts for about 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.

Identification of juveniles is even more problematic, and it is difficult to separate parasitic jaegers from long-tailed jaegers. Parasitic jaegers are bulkier, shorter-winged, and less tern-like than long-tailed jaegers. They are usually warmer toned, with browner shades, rather than grey. However, they show the same wide range of plumage variation. The flight is more falcon-like. The parasitic jaeger is the most common of the three jaeger species seen from shore.

The typical call of these birds is a nasal mewing sound, repeated a few times in display. Their alarm call is a shorter sound.

Distribution and habitat

This species breeds in the north of Eurasia and North America, with significant populations as far south as northern Scotland, in Shetland and Orkney, the Outer Hebrides, Sutherland, Caithness, and some islands in Argyll. Birds in North America breed in Alaska, Yukon, the Northwest Territories, Nunavut, the Hudson Bay coast, and parts of Northern Quebec and Nunatsiavut.

The parasitic jaeger is a migrant, wintering at sea in the tropics and southern oceans. While much of the migration is over sea, overland spring migration occurs in the Canning River Valley, Alaska, and overland fall migration occurs from northern Russia to the Persian Gulf among Eurasian populations, and over the Great Lakes (particularly Lake Ontario) among American populations.

Behavior

Breeding

Nesting occurs on dry tundra, higher fells, and islands. Clutches consist of up to four olive-brown eggs. Jaegers are 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.

Feeding

This bird will feed on rodents, insects, eggs, chicks and small birds in the breeding season, but the majority of its diet (especially in winter and on migration) is made up of food that it acquires by robbing other birds (primarily gulls and terns) of their catches in an act called kleptoparasitism.

Conservation status

In 2018, ''Stercorarius parasiticus'' was regionally uplisted to Endangered in Iceland, from Least Concern in 2000, after their numbers declined drastically in the early 2000s.https://www.ni.is/node/27109 Kristinn Haukur Skarphéðinsson, "Kjói (''Stercorarius parasiticus'')," Icelandic Institute of Natural History, last updated October 2018. It is globally listed as Least Concern.

References

External links

* Arctic skua
Species text in The Atlas of Southern African Birds
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* RSPBbr>Birds by Name: Arctic skua
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Skuas
Cosmopolitan birds
Birds of the Arctic
Holarctic birds
Birds of Scandinavia
Birds of Iceland
Birds of Europe
Birds of Southern Africa
Birds described in 1758
Taxa named by Carl Linnaeus