All species dive. The hind toe has a paddle-like flap. Sexes are unlike. They feed on small aquatic animals and plants.
Sea ducks eat mollusks and crustaceans.
They feed by dabbling and upending and can dive but seldom do. They sometimes feed on land. They swim usually with the tail held off the water. When frightened they spring directly into the air instead of taxiing along the water. Most dabbling species have an iridescent patch on the trailing edge of the wing called a speculum.