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Pomarine Jaeger Life History

Habitat

Habitat Tundra

Pomarine Jaegers breed in areas of the high Arctic that feature lemmings and extensive tundra. They may elect not to breed and may move around considerably in summers when lemming numbers are low. Outside the breeding season they spend their time out at sea, with large numbers in the Caribbean.

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Food

Food Omnivore

During breeding, Pomarine Jaegers specialize on eating brown lemmings, with smaller numbers of other rodents like tundra voles and collared lemmings. Lemming populations cycle over a multiyear period and their population levels can have a strong effect on Pomarine Jaeger breeding. After snowmelt, the birds scan for their prey from small rises in the tundra and fly or run after it. They catch shorebirds, ducks, and ptarmigan infrequently during summer, but the constant threat of predation seems to lower shorebird nest success when jaegers are around. During the nonbreeding season the diet is much more varied, including lemmings, birds, eggs, carrion, insects, fish, squid, and crabs. At sea, they harry kittiwakes, shearwaters, petrels, puffins, terns, boobies, gulls, and other seabirds to steal their catches.

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Nesting

Nest Placement

Nest Ground

Nests on the ground, typically on a slight rise or hummock in the tundra.

Nest Description

Both sexes help trample down a slight depression in the tundra vegetation, sometimes pulling in some nearby vegetation to make a lining.

Nesting Facts

Clutch Size:1-2 eggs
Number of Broods:1 brood
Egg Length:2.2-2.9 in (5.7-7.3 cm)
Egg Width:1.6-1.9 in (4-4.8 cm)
Incubation Period:25-27 days
Nestling Period:2-4 days
Egg Description:

Brown to dark olive-buff, spotted with brown and gray.

Condition at Hatching:

Downy and able to leave the nest in a couple of days.

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Behavior

Behavior Aerial Forager

Although all jaegers are fast, agile fliers, the Pomarine Jaeger is less adept than the smaller Parasitic and Long-tailed. When attacking seabirds to steal their food, Pomarine Jaegers tend to use more brute-force approaches than the acrobatic pursuits of the two smaller species. They can be fairly social at sea, gathering in groups of up to 15 and sometimes sitting on the surface with other seabird species. On breeding territories, Pomarine Jaegers threaten intruders by calling and flying toward them with slow wingbeats, or sometimes stand on the ground and raise their wings, displaying the white flashes in the primaries (outer wings). They also use this wing-raising display when courting mates. Pomarine Jaegers form pair bonds during the breeding season, and both sexes help raise the young.

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Conservation

Conservation Low Concern

Pomarine Jaegers breed in the high Arctic and depend on lemming populations for breeding success—two features that make their numbers difficult to track. Partners in Flight estimates the global breeding population at 1.1 million. They score a 10 out of 20 on the Continental Concern Score, which means they are not on the Partners in Flight Watch List and are a species of low conservation concern.

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Credits

Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.

Haven Wiley, R. and David S. Lee. (2000). Pomarine Jaeger (Stercorarius pomarinus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Mullarney, K., L. Svensson, D. Zetterström, and P. Grant (1999). Collins Bird Guide. HarperCollins Publications Ltd., London, United Kingdom.

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