(Chionididae), a family of birds of the order of plovers. They are 36–43 cm long and white in color. Sheathbills nest in chinks of cliffs and lay two or three spotted pale-brown eggs at a time. They stay near the sea shores, feed on invertebrates (crabs and mollusks) and carrion, and ravage the nests of penguins and stormy petrels.
Because of a number of anatomical peculiarities, sheathbills occupy an intermediary position between pipers and gulls. There are two types: Chionis alba (which has a yellow bill) and Chionis minor (with a black bill). The first is distributed from Tierra del Fuego and the Falkland Islands to the Palmer Archipelago near the northern extreme of Antarctica. The second is found on Kerguélen, Crozet, Prince Edward, Marion, and other islands in the south of the Indian Ocean.