A male Mallard
Duck is the common name for a number of types of bird in the family Anatidae. Ducks are mostly aquatic birds, smaller than their relatives the swans or geese, found in both fresh and salt water. Ducks exploit a variety of food sources such as grasseses, grains and water plants, fish, insects, and the like.
The males (drakes) of northern species often have showy plumage, but this is moulted in summer to give a more female-like appearance, the "eclipse" plumage.
The duck groups are:
- Dendrocygninae: the whistling ducks. There are 9 species in the genus Dendrocygna which has a worldwide distribution through the tropics and subtropics, and a single diving species, Thalassornis leuconotus the White-backed Duck of Africa, which is difficult to classify and has often been placed in the Oxyurinae (which it resembles in morphology and feeding habits). It appears that the similarity is largely a matter of convergence, however.
- Oxyurinae: stiff-tail ducks and Freckled Duck. There are 6 species in the genus Oxyura (the typical stiff-tailed ducks) and three monospecific genera: Biziura (the Australian Musk Duck), Heteronetta (the South American Black-headed Duck which is well known because, cuckoo-like, it is an obligate brood parasite) and Stictonetta (the Freckled Duck of southern Australia).
- Anatinae: perching, diving, and dabbling ducks. The Anatinae are further divided into three groups:
- There are 19 species of perching duck in 15 genera (though the similarities in some are now regarded as convergent, which suggests that a reassignment may be appropriate).
- About 40 species of dabbling duck in 2 genera: the monotypic Marmaronetta (Marbled Teal) may instead be numbered among the pochards. The remaining 40-odd species are all part of the genus Anas, which includes wigeons, gadwalls, the true teals, pintails, mallards, and shovelers.
- The 16 species of pochards or diving ducks in 3 genera: Netta (3 species), Aythya (12 species), and Rhodonessa (the recently extinct Pink-headed Duck of India).
- Merginae: eiders, scoters, sawbills and other sea-ducks. All but two of the 20 species in this group occupy habitats in far northern latitudes. There are 10 genera: Polysticta (Steller's Eider), Somateria (eiders, 3 species), Histrionicus Harlequin Duck, Camptorhynchus (the recently extinct Labrador Duck, Melanitta (the scoters, 3 species), Clangula (the Long-tailed Duck), Bucephala Goldeneyes (3 species), Mergellus Smew, Lophodytes (the Hooded Merganser of North America), and Mergus (the mergansers, 5 species, one extinct).
For further taxonomic comments, see also Sibley-Ahlquist taxonomy.
Ducks should not be confused with several types of unrelated birds with similar forms, such as loons or divers, grebes, gallinules, and coots.