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
Black-tailed gull breeding grounds. The black-tailed gull feeds mainly on small fish, molluscs, crustaceans scraps and carrion. A study analyzing the identifiable parts of gull excreta in Korea found that 19.1% consisted of the remains of fish, 3.3% of crustaceans, and 3.3% of land insects. The species often follows ships and commercial fishing fleets. It also steals food from other seabirds. It is a colonial nester, with colonies forming in mid-April. 2–3 eggs are laid by early June. Incubation lasts approximately 24 days. Black-tailed gulls use a variety of voice signals and are known to use more than 10 different sounds for