The legs are short, strong, and set far to the back of the body (more so in the more aquatic species), and have a leathery feel with a scaly texture.

Combined with their body shape, this can make some species awkward on land, but they are stronger walkers than other marine and water birds such as grebes or petrels.

The bills are made of soft keratin with a thin and sensitive layer of skin on top (which has a leathery feel when touched).

Many of the ducks display sexual dimorphism, with the males being more brightly coloured than the females (although the situation is reversed in species such as the paradise shelduck).

Anatids are vocal birds, producing a range of quacks, honks, squeaks, and trumpeting sounds, depending on species; the female often has a deeper voice than the male.

[3] Anatids are generally herbivorous as adults, feeding on various water-plants, although some species also eat fish, molluscs, or aquatic arthropods.

[4] Anatidae is a large proportion of the 3% of bird species to possess a penis,[5][6] though they vary significantly in size, shape, and surface elaboration.

[3] One aberrant species, the black-headed duck, is an obligate brood parasite, laying its eggs in the nests of gulls and coots.

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 1819.

[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.

Their earliest direct ancestors, though not documented by fossils yet, likewise can be assumed[citation needed] to have been contemporaries with the non-avian dinosaurs.

The following taxa, although certainly new species, cannot be assigned even to subfamily; that Kauaʻi is the oldest of the large Hawaiian Islands, meaning the species may have been evolving in isolation for nearly 10 mya (since the Late Miocene), does not help in determining their affinities: Similarly, Branta rhuax from the Big Island of Hawaiʻi, and a gigantic goose-like anatid from Oʻahu are known only from very incomplete, and in the former case much damaged, bone fragments.

Dendrocheninae – a more advanced relative of the whistling-ducks or an ancestral relative of stifftail ducks paralleling whistling-ducks; if not extinct possibly belong in Oxyurinae (including Malacorhynchus) Anserinae Tadorninae Anatinae Oxyurinae Incertae sedis Putative or disputed prehistoric anatids are: The Middle Oligocene Limicorallus (from Chelkar-Teniz (Kazakhstan) was sometimes considered an anserine.

The middle Eocene Eonessa was formerly thought to belong to Anatidae, however reexamination of the holotype in 1978 resulted in the genus being placed as Aves incertae sedis.