The screamers are three South American bird species placed in family Anhimidae. They were thought to be related to the Galliformes because of similar bills, but are more closely related to the family Anatidae, i.e. ducks and allies,, and the magpie goose, within the clade Anseriformes. The clade is exceptional within the living birds in lacking uncinate processes of ribs. The three species are: The horned screamer ; the southern screamer or crested screamer ; and the northern screamer or black-necked screamer.

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, since swans and geese are not considered ducks. Ducks are mostly aquatic birds, and may be found in both fresh water and sea water.