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
Four-letter word category includes words that are euphemistic evasions of "stronger" words, as well as those that happen to be short and have both an expletive sound to some listeners as well as a sexual or excretory meaning (many also have other, non-vulgar meanings): "" (US), "", "", "" (US), "" (UK, NZ, AUS), "" and "", as several examples. Finally, certain four-lettered terms with limited usage can be considered offensive by some, within the regional dialect in which they are used, such as "" and "mary". Occasionally the phrase "four-letter word" is humorously used to describe common words composed of four