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
Ivory gull Ivory gull The ivory gull ("Pagophila eburnea") is a small gull, the only species in the genus Pagophila. It breeds in the high Arctic and has a circumpolar distribution through Greenland, northernmost North America, and Eurasia. The ivory gull was initially described by Constantine Phipps, 2nd Baron Mulgrave in 1774 as "Larus eburneus" from a specimen collected on Spitsbergen. Johann Jakob Kaup later recognized the unique traits of the ivory gull and gave it a monotypic genus, "Pagophila", in 1829. Johan Ernst Gunnerus later gave the species a new specific name, "Pagophila alba". The genus name "Pagophila" is from Ancient