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 Shrine, and there is a large colony at Teuri Island in Hokkaido. A rare visitor to the United States, a black-tailed gull was spotted from Burlington, Vermont, in October 2005. The species has been spotted in Illinois several times. The species is common on the shoreline of Korea and on various islands. There are over 20,000 black-tailed gulls on Liancourt Rocks, and numbers are increasing due to the absence of predators. In 2008, the bird was officially chosen as one of the mascots of Liancourt Rocks. Nando and Hongdo islands, both Korean natural monuments as of 1982, are also known