information:extraction, stylistic:tone, quality:corruption
Taxonomy

All ducks belong to the biological order Anseriformes, a group that contains the ducks, geese and swans, as well as the screamers, and the magpie goose. All except the screamers belong to the biological family Anatidae. Within the family, ducks are split into a variety of subfamilies and 'tribes'. The number and composition of these subfamilies and tribes is the cause of considerable disagreement among taxonomists. Some base their decisions on morphological characteristics, others on shared behaviours or genetic studies. The number of suggested subfamilies containing ducks ranges from two to five. The significant level of hybridisation that occurs among wild ducks complicates efforts to tease apart the relationships between various species.

In most modern classifications, the so-called 'true ducks' belong to the subfamily Anatinae, which is further split into a varying number of tribes. The largest of these, the Anatini, contains the 'dabbling' or 'river' ducks – named for their method of feeding primarily at the surface of fresh water. The 'diving ducks', also named for their primary feeding method, make up the tribe Aythyini. The 'sea ducks' of the tribe Mergini are diving ducks which specialise on fish and shellfish and spend a majority of their lives in saltwater. The tribe Oxyurini contains the 'stifftails', diving ducks notable for their small size and stiff, upright tails.

A number of other species called ducks are not considered to be 'true ducks', and are typically placed in other subfamilies or tribes. The whistling ducks are assigned either to a tribe (Dendrocygnini) in the subfamily Anatinae or the subfamily Anserinae, or to their own subfamily (Dendrocygninae) or family (Dendrocyganidae). The freckled duck of Australia is either the sole member of the tribe Stictonettini in the subfamily Anserinae, or in its own family, the Stictonettinae. The shelducks make up the tribe Tadornini in the family Anserinae in some classifications, and their own subfamily, Tadorninae, in others, while the steamer ducks are either placed in the family Anserinae in the tribe Tachyerini or lumped with the shelducks in the tribe Tadorini. The perching ducks make up in the tribe Cairinini in the subfamily Anserinae in some classifications, while that tribe is eliminated in other classifications and its members assigned to the tribe Anatini. The torrent duck is generally included in the subfamily Anserinae in the monotypic tribe Merganettini, but is sometimes included in the tribe Tadornini. The pink-eared duck is sometimes included as a true duck either in the tribe Anatini or the tribe Malacorhynchini, and other times is included with the shelducks in the tribe Tadornini.