Gull the exceptions being Sabine's gull and swallow-tailed gulls, which have forked tails, and Ross's gull, which has a wedge-shaped tail. Gulls have moderately long legs, especially when compared to the similar terns, with fully webbed feet. The bill is generally heavy and slightly hooked, with the larger species having stouter bills than the smaller species. The bill colour is often yellow with a red spot for the larger white-headed species and red, dark red or black in the smaller species. The gulls are generalist feeders. Indeed, they are the least specialised of all the seabirds, and their morphology allows for
Sabine's gull species. The two species are thought to have separated around 2 million years ago, longer ago than most groups of gull species. Geographical variation is slight; birds from Alaska are slightly darker and perhaps bigger. Most authorities recognise no races, but a few recognise four based on size and mantle (back) colour. The Handbook of the Birds of the World recognises four subspecies. The nominate subspecies, "X. s. sabini", breeds from the Canadian Arctic to Greenland. "X. s. palaearctica" (Stegman, 1934) breeds from Spitsbergen to the Taymyr Peninsula in Russia, and "X. s. tschuktschorum" (Portenko, 1939) breeds on the Chukotskiy