Waterfowl in U.S. zoos

What makes a waterfowl

Ducks, geese and swans make up the family Anatidae, around 174 species found on every continent except Antarctica. With the magpie goose and three species of screamers, they form the order Anseriformes, one of only two modern bird groups confirmed to have lived alongside the dinosaurs. The southern screamer looks little like a duck, but genetics confirms it is a close relative of geese.

Most waterfowl are built for life on the water surface. Their short, strong legs sit far back on the body, their feet are webbed and special oils make their feathers shed water. The bill is covered in soft, sensitive skin and lined with serrated plates, the lamellae, which are especially well developed in filter-feeders. Sizes range from the cotton pygmy goose, as light as 164 g (5.8 oz), to the trumpeter swan, at up to 17.2 kg (38 lb).

Dabblers, divers, geese and swans

The easiest way to sort ducks is by how they feed. Dabbling ducks, such as the mallard, tip forward to graze plants just under the surface and only rarely dive. The mallard is also the wild ancestor of almost every domestic duck breed. Diving ducks, the pochards and scaups, go fully under; the canvasback can dive more than 9 m (30 ft) deep. Mergansers, such as the hooded merganser, hunt fish underwater with serrated bills.

In many ducks the males are far brighter than the females, as in the mandarin duck and the wood duck, both of which nest in tree holes. Swans, geese and whistling-ducks lack this difference, so males and females look alike. The black swan has the longest neck, relative to its body, of any swan.

Pair bonds vary too. Many small ducks pair for a single season, while swans, geese and some territorial ducks stay together for years. Ducklings and goslings hatch able to feed themselves.

Island ducks and recovery stories

Five duck species have been driven extinct by humans since 1600, most of them island birds with small populations and no fear of predators. Many more are threatened today, and a few species have been domesticated while many others are hunted.

The Laysan duck shows how close an island species can come: by 1912 only twelve birds remained after rabbits stripped their island. It is still Critically Endangered, as is Baer's pochard, an Asian diving duck that may be down to fewer than 1,000 adults. The trumpeter swan fell to fewer than 70 known wild birds by 1933, and reintroduction work has since helped the wild population pass 46,000.