The Anatidae are the biological family of water birds that includes ducks, geese, and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica. These birds are adapted for swimming, floating on the water surface, and in some cases diving in at least shallow water. The family contains around 174 species in 43 genera. (The magpie goose is no longer considered to be part of the Anatidae and is now placed in its own family, Anseranatidae.)

They are generally herbivorous, and are monogamous breeders. A number of species undertake annual migrations. A few species have been domesticated for agriculture, and many others are hunted for food and recreation. Five species have become extinct since 1600, and many more are threatened with extinction.

The name Anatidae for the family was introduced by the English zoologist William Elford Leach in a guide to the contents of the British Museum published in 1820.[8][9] While the status of the Anatidae as a family is straightforward, and which species properly belong to it is little debated, the relationships of the different tribes and subfamilies within it are poorly understood. The listing in the box at right should be regarded as simply one of several possible ways of organising the many species within the Anatidae; see discussion in the next section.

The systematics of the Anatidae are in a state of flux. Previously divided into six subfamilies, a study of anatomical characters by Livezey suggests the Anatidae are better treated in nine subfamilies. This classification was popular in the late 1980s to 1990s. But mtDNA sequence analyses indicate, for example, the dabbling and diving ducks do not belong in the same subfamily.

While shortcomings certainly occur in Livezey's analysis, mtDNA is an unreliable source for phylogenetic information in many waterfowl (especially dabbling ducks) due to their ability to produce fertile hybrids, in rare cases possibly even beyond the level of genus. Because the sample size of many molecular studies available to date is small, mtDNA results must be considered with caution.

While a comprehensive review of the Anatidae which unites all evidence into a robust phylogeny is still lacking, the reasons for the confusing data are at least clear: As demonstrated by the Late Cretaceous fossil Vegavis iaai — an early modern waterbird which belonged to an extinct lineage—the Anatidae are an ancient group among the modern birds. Their earliest direct ancestors, though not documented by fossils yet, likewise can be assumed to have been contemporaries with the non-avian dinosaurs. The long period of evolution and shifts from one kind of waterbird lifestyle to another have obscured many plesiomorphies, while apomorphies apparently are quite often the result of parallel evolution, for example the "non-diving duck" type displayed by such unrelated genera as Dendrocygna, Amazonetta, and Cairina. For the fossil record, see below.

Alternatively, the Anatidae may be considered to consist of three subfamilies (ducks, geese, and swans, essentially) which contain the groups as presented here as tribes, with the swans separated as subfamily Cygninae, the goose subfamily Anserinae also containing the whistling ducks, and the Anatinae containing all other clades.

Taxonomy

For the living and recently extinct members of each genus, see the article List of Anatidae species.

• Subfamily: Dendrocygninae (one pantropical genus, of distinctive long-legged goose-like birds)

  • Dendrocygna, whistling ducks (8 living species)

  • Thalassornis, white-backed duck

    Mute swan

• Subfamily: Anserinae, swans and geese (3–7 extant genera with 25–30 living species, mainly cool temperate Northern Hemisphere, but also some Southern Hemisphere species, with the swans in one genus [two genera in some treatments], and the geese in three genera [two genera in some treatments]. Some other species are sometimes placed herein, but seem somewhat more distinct [see below])

  • Cygnus, true swans (6 species, 4 sometimes separated in Olor)

  • Anser, grey geese and white geese (11 species)

  • Branta, black geese (6 living species)

• Subfamily: Stictonettinae (one genus in Australia, formerly included in the Oxyurinae, but with anatomy suggesting a distinct ancient lineage perhaps closest to the Anserinae, especially the Cape Barren goose)

  • Stictonetta, freckled duck

• Subfamily: Plectropterinae (one genus in Africa, formerly included in the "perching ducks", but closer to the Tadorninae)

  • Plectropterus, spur-winged goose

• Subfamily: Tadorninae – shelducks and sheldgeese

  Male common shelduck

  (This group of larger, often semiterrestrial waterfowl can be seen as intermediate between Anserinae and Anatinae. The 1986 revision[10] has resulted in the inclusion of 10 extant genera with about two-dozen living species [one probably extinct] in this subfamily, mostly from the Southern Hemisphere but a few in the Northern Hemisphere; the affiliations of several presumed tadornine genera has later been questioned[13] and the group in the traditional lineup is likely to be paraphyletic.)

  • Pachyanas, Chatham Island duck (prehistoric)

  • Tadorna, shelducks (6 species, 1 probably extinct) – possibly paraphyletic

  • Radjah, Radjah shelduck

  • Salvadorina, Salvadori's teal

  • Centrornis, Madagascar sheldgoose (prehistoric, tentatively placed here)

  • Alopochen, Egyptian goose and Mascarene shelducks (1 living species, 2 extinct)

  • Neochen, (2 species)

  • Chloephaga, sheldgeese (4 species)

  • Hymenolaimus, blue duck

  • Merganetta, torrent duck

• Subfamily: Aythyinae, diving ducks (Some 15 species of diving ducks, of worldwide distribution, in two to four genera; The 1986 morphological analysis suggested the probably extinct pink-headed duck of India, previously treated separately in Rhodonessa, should be placed in Netta, but this has been questioned. Furthermore, while morphologically close to dabbling ducks, the mtDNA data indicate a treatment as distinct subfamily is indeed correct, with the Tadorninae being actually closer to dabbling ducks than the diving ducks)

  • Netta, red-crested pochard and allies (4 species, 1 probably extinct)

  • Aythya, pochards, scaups, etc. (12 species)

• Subfamily: Anatinae, dabbling ducks and moa-nalos (The dabbling duck group, of worldwide distribution, were previously restricted to just one or two genera, but had been extended to include eight extant genera and about 55 living species, including several genera formerly known as the "perching ducks"; mtDNA on the other hand confirms that the genus Anas is over-lumped and casts doubt on the diving duck affiliations of several genera [see below]. The moa-nalos, of which four species in three genera are known to date, are a peculiar group of flightless, extinct anatids from the Hawaiian Islands. Gigantic in size and with massive bills, they were believed to be geese, but have been shown to be actually very closely related to mallards. They evolved filling the ecological niche of turtles, ungulates, and other megaherbivores.

  • Anas: pintails, mallards, etc. (40–50 living species, 3 extinct)

  • Chendytes, diving-geese (extinct c. 450–250 BCE, A basal member of the dabbling duck clade[16])

  • Spatula, shovelers

  • Mareca, wigeons and gadwalls

  • Lophonetta, crested duck

  • Speculanas, bronze-winged duck

  • Amazonetta, Brazilian teal

  • Sibirionetta, Baikal teal

  • Chelychelynechen, turtle-jawed moa-nalo (prehistoric)

  • Thambetochen, large-billed moa-nalos (2 species, prehistoric)

  • Ptaiochen, small-billed moa-nalo (prehistoric)

 Tribe: Mergini, eiders, scoters, sawbills and other sea-ducks

Common goldeneye couple, male on the right.

(There are 9 extant genera and some 20 living species; most of this group occur in the Northern Hemisphere, but a few [mostly extinct] mergansers in the Southern Hemisphere)

• Shiriyanetta (prehistoric)

• Polysticta, Steller's eider

• Somateria, eiders (3 species)

• Histrionicus, harlequin duck (includes Ocyplonessa)

• Camptorhynchus, Labrador duck (extinct)

• Melanitta, scoters (6 species)

• Clangula, long-tailed duck (1 species)

• Bucephala, goldeneyes (3 species)

• Mergellus, smew

• Lophodytes, hooded merganser

• Mergus, mergansers (4 living species, 1 extinct).

  
  

 Tribe: Oxyurini, stiff-tail ducks (a small group of 3–4 genera, 2–3 of them monotypic, with 7–8 living species)

• Oxyura, stiff-tailed ducks (5 living species)

• Nomonyx, masked duck

• Heteronetta, black-headed duck

• Unresolved: The largest degree of uncertainty concerns whether a number of genera are closer to the shelducks or to the dabbling ducks.

  The rare white-winged duck, a species of unclear affiliation.

  Wood duck Aix sponsa

  See also the monotypic subfamilies above, and the "perching ducks"

  • Coscoroba, coscoroba swan – Anserinae or same subfamily as Cereopsis?

  • Cereopsis, Cape Barren goose – Anserinae, Tadorninae, or own subfamily?

  • Biziura, musk ducks (1 living species)

  • Cnemiornis, New Zealand geese (prehistoric) – as Cereopsis

  • Malacorhynchus, pink-eared ducks (1 living species) – Tadorninae, Oxyurinae or Dendrocheninae?

  • Sarkidiornis, comb duck – Tadorninae or closer to dabbling ducks?

  • Tachyeres, steamer ducks (4 species) – Tadorninae or closer to dabbling ducks?

  • Cyanochen, blue-winged goose – Tadorninae or more distant clade?

  • Nettapus, pygmy geese (3 species) – Anatinae or part of Southern Hemisphere radiation?

  • Pteronetta, Hartlaub's duck – traditionally dabbling ducks, but may be closer to Cyanochen

  • Cairina and Asarcornis, Muscovy duck and white-winged duck, respectively (2 species) – traditionally dabbling ducks, but may be paraphyletic, with one species in Tadorninae and the other closer to diving ducks

  • Aix, Mandarin duck and wood duck (2 species) – dabbling ducks or Tadorninae?

  • Callonetta, ringed teal – dabbling ducks or Tadorninae?

  • Chenonetta, maned duck (1 living species) – dabbling ducks or Tadorninae? Includes Euryanas.

  • Marmaronetta, marbled duck – formerly dabbling ducks; actually a diving duck or a distinct subfamily