Duck is the common name for numerous species of waterfowl in the
family Anatidae. Ducks are generally smaller and shorter-necked
than swans and geese, which are members of the same family. Divided
among several subfamilies, they are a form taxon; they do not
represent a monophyletic group (the group of all descendants of a
single common ancestral species), since swans and geese are not
considered ducks. Ducks are mostly aquatic birds, and may be found
in both fresh water and sea water. Ducks are sometimes confused
with several types of unrelated water birds with similar forms,
such as loons or divers, grebes, gallinules and coots.
