Duck, any of various species of relatively small, short-necked, large-billed waterfowl. In true ducks—i.e., those classified in the subfamily Anatinae in the waterfowl family Anatidae—the legs are placed rearward, as in swans, rather than forward, as in geese. The result is a distinctive waddling gait. Most true ducks, including a few inaccurately called geese (e.g., sheldgeese) by reason of size and build, also differ from swans and true geese.
All true ducks, except those in the shelduck group (the tribe Tadornini) and sea ducks (the tribes Mergini and Somateriini), mature in the first year and pair only for the season—unlike the late-maturing, life-mating true geese and swans. Ducks are generally divided into three major groups, dabbling (shallow-water), diving, and perching ducks, based on their characteristic behaviours. The mallard, a typical dabbling duck (any of about 38 species of Anas and about 5 species in other genera), is one of the most popular game birds.
