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 from the Arctic than adults. Ivory gulls migrate only short distances south in autumn, most of the population wintering in northern latitudes at the edge of the pack ice, although some birds reach more temperate areas. It takes fish and crustaceans, rodents, eggs and small chicks but is also an opportunist scavenger, often found on seal or porpoise corpses. It has been known to follow polar bears and other predators to feed on the remains of their kills. The ivory gull breeds on Arctic coasts and cliffs, laying one to three olive eggs in a ground nest lined with moss,