The Sabine's Gull is a small gull. Its generic placement is disputed; some authors treat it as the sole species in the genus Xema as Xema sabini, while others retain it in the genus Larus as Larus sabini. It breeds in the arctic and has a circumpolar distribution through northernmost North America and Eurasia. It migrates south in autumn; most of the population winters at sea in the Pacific off western South America in the cold waters of the Humboldt Current, while Greenland and eastern Canadian birds cross the Atlantic by way of the westernmost fringes of Europe to winter off southwest Africa in the cold waters of the Benguela Current. Occasionally individual Sabine's Gulls can be seen off other coasts such as the northeastern United States or further east in Europe, typically following autumn storms.

This species is easy to identify through its striking wing pattern. The adult has a pale grey back and wing coverts, black primary flight feathers and white secondaries. The white tail is forked. The male's hood darkens during breeding season. Their bills are black with a yellow tip. Young birds have a similar tricoloured wing pattern, but the grey is replaced by brown, and the tail has a black terminal band. The juveniles take two years to attain full adult plumage. They have a very high-pitched and squeaking call.

The Sabine's Gull breeds in colonies on coasts and tundra, laying two or three spotted olive-brown eggs in a ground nest lined with grass. It is very pelagic outside the breeding season. It takes a wide variety of mainly animal food, and will eat any suitable small prey. It also steals eggs from nesting colonies of Arctic Terns.

The specific epithet and common name honour the Irish scientist Sir Edward Sabine, who had sent a specimen to his brother Joseph Sabine; the first description was in 1819.

Taxonomy and evolution

The Sabine's Gull is usually treated as comprising a monotypic genus, it is only placed within the genus Larus when the genus is enlarged. The black bill and notched tail is almost unique within the gulls, characteristics shared only with the Swallow-tailed Gull of the Galapagos. On the basis of this the two species were often thought to be each other's closest relatives, a hypothesis ruled out by a number of behaviour and ecological differences. Mitochondrial DNA studies confirmed this, and the closest relative of the Sabine's Gull is now thought to be the Ivory Gull, another Arctic species. The two species are thought to have separated a long time ago, around 2 million years ago.

Description

The Sabine's Gull is a small gull, 27–33 cm (11–13 in) in length and weighing 135–225 g (4.8–7.9 oz). The wings are long, thin and pointed with a span of between 81–87 cm (32–34 in). The bill, which is black with a yellow tip, is around 2.5 cm (0.98 in) long.

source: http://en.wikipedia.org/wiki/Xema_sabini

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