Slaty-backed gull

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.[2]

It is tied with the yellow-footed gull for fourth-largest gull species, measuring 55–68.5 cm (21.7–27.0 in) in length, 132–160 cm (52–63 in) in wingspan, and 1.05–1.7 kg (2.3–3.7 lb) in weight.[3][4] Among standard measurements, the wing chord is 40 to 48 cm (16 to 19 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).[4] 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.

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".[5]