Parasitic jaeger (Stercorarius parasiticus)

Also known as: Arctic jaeger, Arctic skua, parasitic skua
  
French: Labbe parasite
KingdomAnimalia
PhylumChordata
ClassAves
OrderCharadriiformes
FamilyStercorariidae
GenusStercorarius (1)
SizeLength: 41 - 46 cm (2)
Wingspan: 110 - 125 cm (2)
Weight330 - 570 g (2)

The parasitic jaeger is classified as Least Concern (LC) on the IUCN Red List (1).

A cunning ocean predator, the parasitic jaeger (Stercorarius parasiticus) is so named for its habit of stealing food from other birds, a behaviour known as ‘kleptoparasitism’ (3). Two different light and dark morphs of the parasitic jaeger exist (4). The light morph has ashy-brown upperparts, whitish underparts, and the sides of its head and neck are yellowish, while in contrast, the dark morph of the parasitic jaeger is uniformly brown all over. Intermediates between these two morphs also exist (4). Most individuals of both morphs have pale or white panels on the underside of the wings (4). 

The parasitic jaeger has a long, wedge-shaped tail, with two thin, pointed feathers which extend beyond the end of the tail (4). The bill, which is slightly hooked (5), is greyish-black, as are the legs (4). 

The male and female parasitic jaeger are similar in appearance (4). Immature birds are usually more yellow-brown than the adults (2), and chicks have dark brown feathery down (4). 

The parasitic jaeger makes a variety of calls, including a long, shrieking call when defending its territory and a short, often repeated call, used especially when attacking or just after landing (6). 

The parasitic jaeger has an astonishingly large distribution, being native to countries in every continent except Antarctica, which it is known to visit (7).

This species is highly migratory, breeding in the Arctic region of the northern hemisphere as far north as Svalbard, and then migrating south to the far southern hemisphere (4) (6). 

An inhabitant of oceans, coastal regions, boreal forest, grassland and tundra (2) (7), the parasitic jaeger shows a great ability to live in windy, wet climates as well as extremely dry and cold ones (2).  

The parasitic jaeger breeds both on islands and on mainland coasts (2), and outside of the breeding season is found mostly at sea (2) (4).

The parasitic jaeger feeds using a method of acquiring food known as kleptoparasitism (6). It chases terns, auks or gulls until the fleeing bird is so distressed that it drops any fish it has recently caught, in order to escape from the parasitic jaeger (3). The jaeger promptly eats this illicitly gained meal by catching it in mid-air or from the surface of the water. The genus name for the parasitic jaeger, Stercorarius, means ‘of or belonging to dung’ in Latin, and originates from an old misconception that it was the pursued bird’s excrement which the jaeger seized from the sky (3).

The jaeger is a talented flier, and is able to manoeuvre with great speed in pursuit of its prey (2). It was the very appropriate inspiration for the Blackburn Skua, the British Fleet Air Arm’s first naval dive-bomber (3). This species is also able to fly into high winds by beating its wings very rapidly and constantly shifting to account for buffeting (2). 

The parasitic jaeger will also eat small birds, rodents, insects, eggs and berries (6).

In April or May, the parasitic jaeger arrives at its northern breeding areas (6), where it breeds in loose colonies (3). The parasitic jaeger attracts a mate through an elaborate flying display. Some pairs mate together repeatedly year after year, while others may switch to a new partner (6). Eggs are laid in May or June (4), usually in a scrape in the ground lined with some twigs or straw (6). Breeding pairs share the duty of guarding the nest and will attack much larger intruders by diving at them at high speed (3) (6). Immature parasitic jaegers begin to leave the breeding habitat soon after they arrive in July (6), while the breeding adults and fledglings remain until August or September (4).

After the breeding season, the parasitic jaeger will initially follow the coast south, often seeming to follow migrating flocks of Arctic terns (Sterna paradisaea), before moving out to sea (2). Most individuals of this species spend the winter near the coasts of South America and western Africa. Many immature individuals spend their first two years in wintering areas, before returning to the breeding grounds (4).

Due to its extremely large range and its very large and generally stable population, the parasitic jaeger is not considered to be an endangered species (7).

However, it does still face threats in some parts of its range. In Britain, numbers of the parasitic jaeger have recently declined, perhaps due to the over-fishing of sandeels on which it feeds around Orkney and Shetland (3). In the 1980s, parasitic jaegers were shot illegally on Fair Isle in Shetland because it was believed that their dive-bombing disturbed grazing sheep and even occasionally drove the sheep over cliff edges (3). 

There are currently no specific conservation efforts in place for the parasitic jaeger.

Find out more about the parasitic jaeger:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
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  1. IUCN Red List (November, 2010)
    http://www.iucnredlist.org/
  2. Snow, D.W. and Perrins, C.M. (1998) The Birds of the Western Palearctic. Oxford University Press, Oxford.
  3. Cocker, M. and Mabey, R. (2005) Birds Britannica. Chatto & Windus, London.
  4. Harrison, P. (1985) Seabirds: An Identification Guide. Revised Edition. Christopher Helm, London.
  5. Tuck, G.S. (1978) A Field Guide to the Seabirds of Britain and the World. Collins, London.
  6. O’Donald, P. (1983) The Arctic Skua: a Study of the Ecology and Evolution of a Seabird. Cambridge University Press, Cambridge.
  7. BirdLife International (November, 2010)
    http://www.birdlife.org/datazone/speciesfactsheet.php?id=3201