The Anatidae are the biological family of birds that includes ducks, geese and swans. The family has a cosmopolitan distribution, occurring on all the world's continents. These are birds that are adapted through evolution for swimming, floating on the water surface, and in some cases diving in at least shallow water. (The magpie goose is no longer considered to be part of the Anatidae, but is placed in its own family Anseranatidae.) The family contains around 146 species in 40 genera.