Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans. Some definitions of the term 'waterfowl' include the saltwater shorebirds or waders, gulls, pelicans, and herons, as well as seabirds such as the albatross, but 'fowl' especially refers to birds used by humans for game. They have historically been an important food source, and continue to be hunted as game, or raised as poultry for meat and eggs and are sometimes kept as pets.
They are strong swimmers with medium to large bodies with webbed feet and a broad, flat and somewhat rounded-tip bill. Some species dive deep for fish or mollusks, others feed near the surface or filter through shallow bottom sediments. Some even graze on land. Most species of waterfowl are migratory. The fossil of the bird Presbyornis shows a long-legged shorebird-like form witha duck-like bill. This fossil, which is some 50 million years old, may suggest an evolutionary relationship between Anseriformes and shorebirds. 
^Alice E. Mace, Suzanne Sherman, Ron Hildebrand, Linda Bouchard, Pam Peirce, John Dawson (1986). The Birds Around US (Hardcover ed.). Ortho Books. p. 33. ISBN0-89721-068-9.|accessdate= requires |url= (help)