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
Glaucous gull Glaucous gull The glaucous gull ("Larus hyperboreus") is a large gull, the second largest gull in the world, which breeds in Arctic regions of the Northern Hemisphere and winters south to shores of the Holarctic. The genus name is from Latin "Larus", which appears to have referred to a gull or other large seabird. The specific "hyperboreus" is Latin for "northern" from the Ancient Greek "Huperboreoi" people from the far north "Glaucous" is from Latin "glaucus" and denotes a bluish-green or grey colour. This gull is migratory, wintering from in the North Atlantic and North Pacific oceans as far south