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
Fork-tailed storm petrel visible. The distinguishing feature of fork-tailed storm petrels is their overall bluish-gray plumage. They generally have a paler underside, which contrasts the darker colours under its wing. They also have a dark gray forehead, a black ear patch, and a small black bill. Other storm petrels are significantly darker, such as the similar looking Ashy storm petrel.. However, fork-tailed storm petrels from southern populations are somewhat darker than those in the north. Males and females of this species are generally very similar in colour and size. Juveniles also resemble adults with the exception of having a less noticeable notch in