Ducks, geese and swans belong to one ancient and surprisingly varied family
From a cotton pygmy goose weighing about 164 grams to a trumpeter swan of up to 17.2 kilograms, the waterfowl family Anatidae spans a huge size range. Its roughly 174 species live on every continent but Antarctica, and its ancestors probably shared the planet with the last non-bird dinosaurs.
Most members share a broad body, a long neck, short legs set well back, and webbed feet, though the Hawaiian nene has lost much of its webbing. Their bills are soft keratin covered by a thin sensitive skin and lined with comb-like ridges, sharpest in filter feeders. Special oils make their feathers shed water. Adults mostly eat water plants, but mergansers use serrated bills to catch fish. Voices range from quacks and honks to trumpeting, and in many species the female sounds deeper than the male.
Breeding habits vary. Many small ducks pair for one season only, while swans and geese often stay together for years or life. Nests are simple, usually lined with down the mother plucks from her own breast, and the chicks can feed themselves from hatching. The black-headed duck of South America never raises young at all; it slips its eggs into the nests of gulls and coots.
Sorting out family relationships remains messy. The English zoologist William Elford Leach named the family in 1819, but proposals have ranged from three subfamilies to nine, and genetic studies show that dabbling and diving ducks do not belong together. A Late Cretaceous waterbird, Vegavis, hints at how old the lineage is, and long evolution plus repeated parallel changes have blurred the clues. Among the strangest relatives were Hawaii's extinct moa-nalos, giant flightless birds long mistaken for geese that turned out to be close kin of mallards.
People have eaten these birds and stuffed pillows with their down for a long time, and a few species were domesticated. Since 1600, five duck species have vanished through human activity, mostly tame island birds that had lost the urge or ability to fly. Introduced species also cause trouble: in Europe, the ruddy duck interbreeds with and threatens the native white-headed duck.
Source: Anatidae
