Stercorariidae Skuas and Jaegers
Version: 1.0 — Published March 4, 2020
Introduction
As their common name suggests (“jaeger” is German for hunter), these birds with strong hooked bills are raptorial birds of the open sea. Jaegers and skuas are relentless predators and pirates, terrorizing other seabirds in the vicinity by taking their eggs and chicks or stealing their captured prey. At their own nests, however, jaegers are model parents, protecting their young with a combination of attacks and distraction displays and feeding them a rich diet of smaller vertebrates throughout their nestling life. Like raptors, female skuas and jaegers are larger, and some skuas commonly form breeding associations of one female and two males (or more) raising the same brood together.
Habitat
During the breeding season, skuas and jaegers nest on tundra or on open grassy or bare-rock areas on islands. Outside the breeding season, most species spend most of their time at sea out of sight of land.
Diet and Foraging
Stercorariids have a varied diet of animal prey, opportunistically hunting, scavenging, or kleptoparasitizing. During the breeding season, some species feed more on fish than others, while some eat a great many lemmings, and others eat mostly eggs and chicks of other species. But during the non-breeding season their diet is mostly fish, which they either catch themselves or steal from other birds.
Breeding
Skuas and jaegers are mostly monogamous with biparental care. Some populations of Brown Skua Catharacta antarctica exhibit cooperative polyandry, with one female breeding with multiple (typically two, but sometimes up to six) males. In these polyandrous groups, only a single nest is tended, and all the males associating with the female assist in territory defense, incubation, and feeding chicks. Stercorariid nests are simple structures, consisting of a small scrape or depression on the ground in which females lay 1 or 2 eggs. Location of the nest varies with species, and may be on bare rock or on tundra-like ground with vegetative cover limited to small bushes and grass. Both parents participate in nest construction (by trampling the ground to create a depression), incubation, feeding chicks, and territory defense. Parents regurgitate food for the chicks or tear off pieces of prey for them. The precocial chicks hatch after 24 to 32 days of incubation, and they stay near the nest, where they are fed until they fledge after 24 to 50 days.
Conservation Status
No species of jaegers or skuas face immediate conservation concerns.
Systematics History
Stercorariidae is part of the suborder Lari of Charadriiformes. Although most morphological studies group these birds with the gulls in an expanded Laridae (Cracraft 1981, Chu et al. 2009), the classification of Stercorariidae has varied. One molecular phylogenetic study based on mitochondrial DNA found gulls and jaegers to be sister groups (Cohen et al. 1997), whereas more recent analyses of more extensive molecular datasets have suggested instead that Stercorariidae is sister to Alcidae (Baker et al. 2007a, Fain & Houde 2007, Pereira & Baker 2010). At least one recent morphological study (Mayr 2011) supported this hypothesis, with some skeletal features, including skull characters, suggesting the same sister relationship.
Conservation Status
Least Concern |
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Near Threatened |
0%
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Vulnerable |
0%
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Endangered |
0%
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Critically Endangered |
0%
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Extinct in the Wild |
0%
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Extinct |
0%
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Not Evaluated |
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Data Deficient |
0%
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Unknown |
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Data provided by IUCN (2023) Red List. More information