Stercorarius

Stercorarius
Name	Stercorarius
Taxon	Stercorarius
Authority	Brisson, 1760
Type species	Stercorarius parasiticus
Subdivision ranks	Species
Subdivision	See text.

Stercorarius. The genus Stercorarius comprises the seabirds commonly known as skuas or jaegers, belonging to the family Stercorariidae. These medium-to-large birds are renowned for their aggressive, piratical feeding behavior, often harassing other seabirds to steal their catch. They are strong, acrobatic fliers with a circumpolar distribution, breeding in the high latitudes of both hemispheres and migrating vast distances across the world's oceans.

Taxonomy and systematics

The genus Stercorarius was formally introduced in 1760 by the French zoologist Mathurin Jacques Brisson. The name is derived from the Latin stercus, meaning "dung", a reference to the historical belief that these birds defecated on other species. Modern phylogenetics places the genus within the order Charadriiformes, closely related to gulls, terns, and auks. Significant taxonomic revisions have occurred, with some authorities, like the American Ornithological Society, historically merging the smaller jaegers into the genus Catharacta before recent DNA sequencing studies supported a unified Stercorarius. The type species is the Parasitic Jaeger (Stercorarius parasiticus). Ongoing research involving mitochondrial DNA continues to clarify relationships within the genus and its sister taxa.

Description and morphology

Skuas are robust, gull-like birds with long, pointed wings and a powerful, hooked bill. They exhibit pronounced sexual dimorphism, with females generally larger than males. Most species display two color morphs: a dark morph and a paler morph, with the latter often showing a distinctive pale neck. All species have central tail feathers that are elongated and pointed in adults, particularly noticeable in the breeding plumage of the jaeger species. Their legs are webbed, and they possess sharp claws, adaptations for their predatory and kleptoparasitic lifestyle. The Great Skua (Stercorarius skua) is the largest, with a wingspan often exceeding 140 cm, while the Long-tailed Jaeger (Stercorarius longicaudus) is the smallest and most graceful.

Distribution and habitat

Stercorarius species have a circumpolar distribution, primarily associated with the Arctic and Antarctic regions. They breed on open tundra, coastal moorlands, and barren islands in the high latitudes of the Northern Hemisphere and around the coast of Antarctica. Outside the breeding season, they become highly pelagic, undertaking some of the longest migrations of any bird. For example, the Arctic Skua (Stercorarius parasiticus) migrates from its breeding grounds in the Arctic Circle to wintering areas as far south as the Southern Ocean. They are commonly sighted over open ocean, often following shipping lanes or fishing fleets.

Behavior and ecology

Skuas are opportunistic feeders and notorious for kleptoparasitism, vigorously chasing birds like terns, gulls, and gannets to force them to disgorge their food. They are also capable predators, taking fish, small mammals, eggs, and the chicks of other seabirds, including those of penguins in the south. Breeding pairs are highly territorial and defend their nests aggressively against intruders, including humans. They are typically monogamous and exhibit biparental care. Some species, like the South Polar Skua (Stercorarius maccormicki), are known for their long-distance migrations between the Arctic and Antarctic.

Species list

The genus contains seven widely recognized extant species: * Great Skua or Bonxie (Stercorarius skua) * Brown Skua (Stercorarius antarcticus) * South Polar Skua (Stercorarius maccormicki) * Pomarine Jaeger (Stercorarius pomarinus) * Parasitic Jaeger or Arctic Skua (Stercorarius parasiticus) * Long-tailed Jaeger (Stercorarius longicaudus) * Chilean Skua (Stercorarius chilensis)

Relationship with humans

Skuas have a complex relationship with humans. On breeding grounds, they are known to dive-bomb researchers or tourists who venture too close to their nests. They have historically been persecuted by fishermen and egg collectors. Some populations, particularly of the Great Skua, have benefited from the discards of commercial fishing operations in the North Sea. They are considered indicators of marine ecosystem health and are studied in long-term monitoring programs like those conducted by the British Antarctic Survey. Their aggressive nature and dramatic aerial pursuits make them a notable subject for birdwatchers and wildlife photographers in regions such as Shetland and Spitsbergen.

Category:Stercorariidae Category:Bird genera