Sabine's gull treated as comprising a monotypic genus; it is only placed within the genus "Larus" when the genus is enlarged. The black bill and notched tail are almost unique within the gulls, as they are shared only with the swallow-tailed gull of the Galapagos. On the basis of this the two species were often thought to be each other's closest relatives, a hypothesis ruled out by a number of behaviour and ecological differences. Mitochondrial DNA studies confirmed that they are not closely related, and the closest relative of the Sabine's gull is now thought to be the ivory gull, another Arctic
Thayer's gull Iceland gull. Both the common and species names honor ornithologist John Eliot Thayer, and so the first part of its name is pronounced "THAY-erz". Thayer's gull Thayer's gull ("Larus glaucoides thayeri") is a subspecies of the Iceland gull. It is a large gull native to North America that breeds in the Arctic islands of Canada and winters primarily on the Pacific coast, from southern Alaska to the Gulf of California, though there are also wintering populations on the Great Lakes and the upper Mississippi River. The species has occurred as a vagrant to Japan, Denmark, and other parts of western