Anatidae includes the ducks, geese and swans. The family occurs on all the world's continents except Antarctica and on most of the world's islands and island groups. These are birds that are adapted for swimming, floating on the water surface, and in some cases diving in at least shallow water. The family contains around 146 species in 40 genera. They are generally herbivorous. 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 ducks, geese and swans are small to large sized birds that have a general body plan that is broad and elongated. Diving species vary from this in being rounder. The wings are short and pointed, and supported by strong wing muscles that generate rapid beats in flight. They typically have long necks, although this varies in degree between species. The legs are short and strong and set far to the back of the body, more so in the more aquatic species. 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. They have webbed feet. The bills of most species are flattened to a greater or lesser extent. These contain serrated lamellae which are particularly well defined in the filter-feeding species.
Their feathers are excellent at shedding water due to special oils. Many of the ducks display sexual dimorphism, with the males being more brightly coloured than the females. The swans, geese and whistling-ducks lack sexually dimorphic plumage. 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.