Bonaparte's gull (Chroicocephalus philadelphia) is a member of the gull family Laridae found mainly in northern North America. At in length, it is one of the smallest species of gull. Its plumage is mainly white with grey upperparts. During breeding season, Bonaparte's gull gains a slaty-black hood. The sexes are similar in appearance. Taxonomy and etymology When George Ord first described Bonaparte's gull in 1815, he gave it the scientific name Sterna philadelphia, assigning it to the genus now used for medium-sized terns. Most later taxonomists assigned it to the genus Larus, a longtime catch-all for most of the gull species. However, in 1858, George Newbold Lawrence moved the species to the genus Chroicocephalus, and some taxonomists followed suit. Recent molecular DNA studies have shown that this species fits neatly into a clade with other "masked gulls", and that it and the slender-billed gull are each other's closest relatives and are basal to the rest of that grouping. Based on these studies, the American Ornithologists' Union, which had previously assigned the species to the genus Larus, moved it into its current genus in 2008. It is monotypic across its range. The species is named for Charles Lucien Bonaparte, a French ornithologist (and nephew to the former French emperor Napoleon Bonaparte) who spent eight years in America, contributing to the understanding of the taxonomy and nomenclature of birds there and elsewhere. Its genus name, Chroicocephalus, is a combination of the Greek words , an adjective form of meaning "colour", and meaning "head". This refers to the dark heads that gulls of this genus show during the breeding season. The specific epithet philadelphia is a Latinized adjective meaning "from Philadelphia", a reference to the location from which the type specimen was collected. Description Bonaparte's gull is among the smallest of the gull species; only little gull and Saunders's gull are smaller. Adults range from in length, with a wingspan of and a body mass of . There is no difference in plumage or bare part colour between the sexes, though males tend to be heavier than females. Bonaparte's gull is smaller-bodied, smaller-headed, and smaller-billed than the other common hooded gulls of North America. The adult has grey upperparts and white underparts; its wingtips are black above and pale below. In breeding plumage, it has a slaty black hood, which it loses in non-breeding plumage. Its short, thin bill is black, and its