the slaty-backed gull (larus schistisagus) is a large white-headed gull that breeds on the western coast of alaska 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 .
the slaty-backed gull is tied with the yellow-footed gull (larus livens) for the fourth largest species of gull in the world .
it is considered the north pacific equivalent of the largest gull species , the great black-backed gull .
measuring 5568.5 cm (21.727.0 in) in length , 132160 cm (5263 in) in wingspan and weighing 1.051.7 kg (2.33.7 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 .
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 .
like other gulls , the slaty-backed gull is both a forager and a scavenger .
