Waterfowl

Ducks, swans, and geese make up the rather uniform order Anseriformes. These birds have webbed feet and a bill that is usually broad, flat, and somewhat rounded at the tip. Distributed worldwide, these water fowl usually feed on aquatic plants and animals. Some species dive deep for fish or mollusks, others feed at or near the surface, some filter through shallow bottom sediments, and others even graze on land. Most species of waterfowl are migratory. Offshoots of the order are three species of South American screamers, which are more terrestrial and have chicken-like bills. The fossil of the bird Presbyornis shows a long-legged shorebird-like form with a duck-like bill. This fossil. which is some 50 million years old, may suggest an evolutionary relationship between Anseriformes and shorebirds.