Thai National Parks

The slaty-backed gull (Larus schistisagus) is a large, white-headed gull that breeds on the north-eastern coast of the Palearctic, but travels widely during nonbreeding seasons. It is similar in appearance to the western gull and the glaucous-winged gull. Another alternate name is Pacific gull, though this also applies to a Southern Hemisphere species, L. pacificus. Claims have been made as to its (sometimes occasional) presence throughout North America. as well as the eastern coast of temperate Asia (Palearctic). On 3 November 2012, an individual was spotted in Finland. The species has only been spotted three times before in Europe.

This species is tied with the yellow-footed gull for fourth-largest gull species. This species measures 55 - 68.5 cm in length, 132 - 160 cm in wingspan, and 1.05 - 1.7 kg in weight. Among standard measurements, the wing chord is 40 to 48 cm, the bill is 4.8 to 6.5 cm, and the tarsus is 6 to 7.6 cm. It has a white head, belly, and tail with a dark slaty-gray back and wings with a broad white trailing edge. The wings and back are slightly darker than those of the western gull. The undersides of the wings feature a "string of pearls" pattern along their edges; these can be seen from below when the bird is in flight. Its eyes are yellow. The legs are pink and short when compared with those of similar-looking gulls, and the body appears more stout. The bill is yellow with orange-red subterminal spot (the spot near the end of the bill that chicks peck to stimulate regurgitative feeding). Immature gulls' plumage is brown, similar to that of the great black-backed gull, but paler, and is practically indistinguishable from the immature herring gull in the field.

Etymology

The genus name is from Latin larus, which appears to have referred to a gull or other large seabird. The specific schistisagus is from New Latin schistus, "slate", and Latin sagus, "cloak".

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