Ivory gull narrower os pubis, and potentially more flexibility in skull kinetic structure. Structurally, it is most similar to the kittiwakes; however, recent genetic analysis based on mtDNA sequences shows that Sabine's gull is the ivory gull's closest relative, followed by the kittiwakes, with Ross's gull and swallow-tailed gull sharing a clade with these species. "Pagophila" is maintained as a unique genus because of the bird’s morphological, behavioral and ecological differences from these species. Colloquial names from Newfoundland include slob gull (from "slob", a local name for drift ice) and ice partridge, from a vague resemblance to a ptarmigan. This species is
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