The order Anseriformes contains about 150 living species of birds in three families: the Anhimidae (the screamers), Anseranatidae (the Magpie Goose), and the Anatidae, which includes over 140 species of waterfowl, among them the ducks, geese, and swans. All species in the order are web-footed for efficient swimming and have a large wide bill with a specialized tongue that allows water to be sucked in the front of the bill. An array of plates traps food particles as the water is expelled out the sides of the bill. Not all species feed this way, some graze on plants and some also catch fish. [abstracted from Wikipedia]