The parasitic jaeger or arctic jaeger ( Stercorarius parasiticus), also known as the parasitic skua or arctic skua in Europe, is a seabird in the skua family Stercorariidae. It is a migratory species breeding in Northern Fennoscandia, Scotland, Iceland, Greenland, Northern Canada, Alaska, and Siberia and wintering 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 language word
Jäger, meaning "hunter".
The English "skua" comes from the
Faroese language 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.
Arctic skua (Stercorarius parasiticus) in flight Keflavíkurbjarg.jpg|Dark morph in Iceland
Arctic skua (Stercorarius parasiticus) in flight Keflavíkurbjarg 2.jpg|Dark morph in Iceland
ArcticSkua3.jpg|immature in India
2021-07-11 Parasitic jaeger - 51358219005.jpg|Light morph in Alaska
Distribution and habitat
This species breeds in the north of Palearctic 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 bird migration, 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 , 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 (primarily and ) of their catches in an act called kleptoparasitism.
Conservation status
In 2018, Stercorarius parasiticus
Kristinn Haukur Skarphéðinsson, "Kjói ( Stercorarius parasiticus)," Icelandic Institute of Natural History, last updated October 2018. It is globally listed as Least Concern.
External links
