Tuesday 21 May
Pomarine jaeger (Stercorarius pomarinus)
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Pomarine jaeger fact file
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Pomarine jaeger description
The largest of the jaegers, the pomarine jaeger (Stercorarius pomarinus) is most distinctive in the summer, when it bears unusual spoon-shaped central tail feathers measuring up to 11 centimetres. These tail streamers are lost in the winter months, which can often make the adults difficult to distinguish from the juveniles (2) (4).
Pomarine jaeger adults may either be a light or dark morph. The majority of adults are the ‘light’ form, having dark brown upperparts and white underparts with a bold brown bar stretching across the chest. The top of the head is black and it has a bright white collar with a yellowish tinge on the sides of the neck. The underside of the wings fade from dark brown to white, with the edges becoming darker again (4). Dark morph adults are similar except the underparts, collar and sides of the neck are dark brown (4).
Juvenile pomarine jaegers differ in appearance to the adults, being brown all over except for the underparts which are patterned with blackish bars (4).
The name ‘pomarine’ originally comes from a Greek word meaning ‘lid-nosed’. This is due to the fact that the bird has a pale, saddle-like covering on the base of the upper bill which gives it a two-tone effect (4).
- Also known as
- pomarine skua.
- Labbe pomarin.
- Head-body length: 46 - 51 cm (2)
- Wingspan: 125 - 138 cm (2)
- Male weight: 648 g (3)
- Female weight: 745 g (3)
- The flesh of a dead animal.
- Kept warm so that development is possible.
- One of two or more distinct types of a given species, often distinct colour forms, which occur in the same population at the same time (that is, are not geographical or seasonal variations).
- An area occupied and defended by an animal, a pair of animals or a colony.
- Treeless, grassy plains characteristic of arctic and sub-arctic regions. They are very cold and have little rainfall.
IUCN Red List (November, 2010)
- del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
- Maher, W.J. (1970) The pomarine jaeger as a brown lemming predator in northern Alaska. The Wilson Bulletin, 82(2): 130-157.
U.S. Fish and Wildlife Service (November, 2010)
BirdLife International (November, 2010)
- Pitelka, F.A., Tomich P.Q. and Treichel G.W. (1955) Breeding behaviour of jaegers and owls near Barrow, Alaska. The Condor, 57(1): 3-18.
- Maher, W.J. (1974) Ecology of Pomarine, Parasitic and Long-tailed Jaegers in Northern Alaska. Cooper Ornithological Society, Los Angeles, California.
- Andersson, M. (1973) Behaviour of the pomarine skua Stercorarius pomainus Temm. with comparative remarks on Stercorariinae. Ornis Scandinavica, 4(1): 1-16.
- Custer, T.W. and Pitelka, F.A. (1987) Nesting by pomarine jaegers near Barrow, Alaska, 1971. Journal of Field Ornithology, 58(2): 225-230.
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Pomarine jaeger biology
During the breeding season, between May and September (2) (5), the pomarine jaeger is highly dependent on the availability of its main food source, lemmings. Lemming populations grow and shrink cyclically every three to five years, and the pomarine jaeger only successfully reproduces when lemming populations peak (6).
The pomarine jaeger catches lemmings by chasing them across the ground and, if the lemming tries to evade the bird by entering its burrow, the pomarine jaeger will tear at the burrow with its beak to reach the lemming inside (8). The pomarine jaeger is the only avian predator which will dig for the lemming in this manner (4). It will also prey on other types of rodent (3) and when these are in short supply it will eat small birds (3) (9). Outside of the breeding season the pomarine jaeger eats a smaller number of rodents and instead eats more birds, carrion, fish and insects (3), which it obtains not only by scavenging and hunting, but also by stealing from other birds (4).
The pomarine jaeger builds its nest on marshy flat land (6). The female usually lays 2 eggs which are incubated for 25 to 27 days (6). The chicks leave the nest just two days after hatching (7), but it takes a further month for their feathers to become fully developed and for them to be able to fly (6).
When protecting its breeding territory the pomarine jaeger has a very nasal call and will simultaneously flap its wings higher up and more slowly than usual. If the intruder is not deterred, the pomarine jaeger will call and start to glide with its wings held in the shape of a ‘V’ to scare off the intruder. This species may also give a short call or a call that fluctuates in pitch to warn when predators are approaching (8).Top
Pomarine jaeger range
The pomarine jaeger breeds in the far northern reaches of Europe, Asia and America (2) (5). In the winter, the pomarine jaeger migrates to areas between the Tropic of Capricorn and the Tropic of Cancer, as well as along the coasts of Argentina and Australia (5).Top
Pomarine jaeger habitatTop
Pomarine jaeger status
The pomarine jaeger is classified as Least Concern (LC) on the IUCN Red List (1).Top
Pomarine jaeger threats
Although the pomarine jaeger is not currently considered to be threatened with extinction (1), its dependence on lemmings does place it in a vulnerable situation. As the pomarine jaeger tends to not breed when there is a low lemming population (6) (9), any future threats to the lemmings will also impact greatly on the jaeger (4).
Other potential future threats include climate change, which could alter the pomarine jaeger's favoured habitats (5).Top
Pomarine jaeger conservation
Currently, there are no known conservation measures in place for the pomarine jaeger.Top
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