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
Swallow-tailed gull Swallow-tailed gull The swallow-tailed gull ("Creagrus furcatus") is an equatorial seabird in the gull family, Laridae. It is the only species in the genus Creagrus, which derives from the Latin "Creagra" and the Greek "kreourgos" which means butcher, also from "kreas", meat; according to Jobling it would mean "hook for meat" referring to the hooked bill of this species. It was first described by French naturalist and surgeon Adolphe-Simon Neboux in 1846. Its scientific name is originally derived from the Greek word for gull, "Glaros" and via Latin "Larus", "gull" and "furca" "two-tined fork". It spends most of its life