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
Kumlien's gull Kumlien's gull Kumlien's gull ("Larus glaucoides kumlieni") is a large gull which breeds in the Arctic regions of Canada. It is migratory, wintering from Labrador south to New England and west across the Great Lakes. The species is named after the Swedish-American naturalist Thure Kumlien. It is a regular vagrant in small numbers to Britain and Ireland. It has variably been considered a full species, a subspecies of Thayer's gull, a subspecies of Iceland gull, and a hybrid between the aforementioned species, all of which are considered subspecies of the Iceland gull as of 2017. This taxon breeds colonially or