The slaty-backed gull (Larus schistisagus) is a large white-headed gull that breeds on the north-eastern coast of Asia 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, Larus pacificus. Claims have been made as to its (sometimes occasional) presence throughout North America as well as the eastern coast of Asia. On November 3, 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. Measures 55–68.5 cm (21.7–27.0 in) in length, 132–160 cm (52–63 in) in wingspan and weighs 1.05–1.7 kg (2.3–3.7 lb). Among standard measurements, the wing chord is 40.6 to 48 cm (16.0 to 18.9 in), the bill is 4.8 to 6.5 cm (1.9 to 2.6 in) and the tarsus is 6 to 7.6 cm (2.4 to 3.0 in). 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 underside of the wings features 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 in order 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.