Bonaparte's gull (Chroicocephalus philadelphia) is named after French biologist and ornithologist Charles Lucien Bonaparte – nephew to the former French emperor Napoleon Bonaparte. Charles Bonaparte spent eight years in America, contributing to the understanding of the taxonomy and nomenclature of birds. It is among the smallest of the gull species – only the little gull and Saunders's gull are smaller. The adult has grey upperparts and white underparts; its wingtips are black above and pale below. It has a slaty black hood, but only in breeding plumage. The genus name, Chroicocephalus, is a combination the Greek words meaning colour and head. Philadelphia is where the type specimen was collected.