pomarine skua

pomarine skua
Name	Pomarine skua
Genus	Stercorarius
Species	pomarinus
Authority	(Linnaeus, 1766)

pomarine skua. The pomarine skua is a large, powerful seabird of the family Stercorariidae, known for its distinctive twisted central tail feathers in breeding plumage. It breeds on the high Arctic tundra of North America and Eurasia and undertakes remarkable long-distance migrations across the world's oceans. This formidable predator and kleptoparasite is a striking presence in both its remote breeding grounds and its pelagic wintering areas.

Description and taxonomy

The species was first formally described by Carl Linnaeus in the 10th edition of Systema Naturae in 1766. It is placed within the genus Stercorarius, which includes all skuas and jaegers. The pomarine skua exhibits pronounced sexual dimorphism, with females being larger and heavier than males. Two color morphs exist, a dark morph and a more common pale morph, with considerable individual variation. Its most diagnostic feature is the elongated, spoon-shaped central tail feathers, which are twisted and visible only in adult breeding plumage. The bird's powerful flight is aided by long, broad wings, and it has a robust, hooked bill typical of an avian predator.

Distribution and habitat

Its breeding range is circumpolar, encompassing the northernmost tundra regions of Siberia, Alaska, the Canadian Arctic Archipelago, and islands like Svalbard and Franz Josef Land. During the breeding season, it exclusively inhabits open, treeless Arctic landscapes, often near wetlands or coastal areas. Outside of breeding, it becomes entirely pelagic, migrating across the Atlantic Ocean, Pacific Ocean, and Indian Ocean. It winters as far south as the waters off South Africa, Australia, New Zealand, and Peru, frequenting upwelling zones and continental shelves rich in marine life.

Behavior and ecology

The pomarine skua is a highly aerial and aggressive bird, often engaging in dramatic aerial pursuits. It is a noted kleptoparasite, relentlessly harassing other seabirds such as fulmars, terns, and kittiwakes to force them to disgorge their food. This behavior is most frequently observed along migration routes and on wintering grounds. On its breeding territory, it is highly territorial and will aggressively defend its nest from predators like the Arctic fox and other skuas. Its flight is direct and powerful, capable of covering vast oceanic distances during its transequatorial migrations.

Diet and feeding

Its diet is exceptionally varied and opportunistic. During the summer on the tundra, it preys heavily on lemmings and voles, and will also take eggs and chicks of other birds, including geese and shorebirds. At sea, its diet shifts to fish, often obtained through kleptoparasitism from auks, puffins, and gannets. It also scavenges, follows fishing vessels for offal, and directly catches small marine organisms like krill. The abundance of rodents on the tundra is a critical factor influencing its breeding success and population cycles.

Breeding

Breeding occurs in loose, scattered colonies on the open tundra. The nest is a simple shallow scrape on the ground, often on a raised hummock or ridge. A typical clutch consists of two olive-brown eggs, which are incubated by both parents for about 25-30 days. The precocial chicks leave the nest within two days but remain in the territory, where they are fed by their parents. The breeding cycle is tightly linked to the population cycles of Arctic rodents; in poor lemming years, many pairs may not attempt to breed at all. Families depart the breeding grounds by early autumn for their marine wintering areas.

Conservation status

The International Union for Conservation of Nature lists the pomarine skua as a species of Least Concern due to its extremely large range and population. However, its reliance on specific and vulnerable ecosystems makes it susceptible to broader environmental changes. Potential threats include climate change affecting its Arctic breeding habitat and prey availability, pollution in marine environments, and incidental bycatch in fisheries. It is protected under the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), which aims to coordinate conservation efforts across its migratory range.

Category:Stercorariidae Category:Birds of the Arctic Category:Birds described by Carl Linnaeus