Geese Ducks Swans and Screamers: Anseriformes

Waterfowl, including ducks, geese, and swans, vary greatly in size and weight. The smallest is the tropical pygmy-goose, which weighs just 10 ounces (269 grams) and stands 12 inches (30 centimeters) tall. The largest is the trumpeter swan, which stands at 72 inches (183 centimeters) and weighs more than 38 pounds (17 kilograms). Screamers are large birds, standing 30 to 37 inches (76 to 95 centimeters) and weighing anywhere from 6 to 88 pounds (3 to 40 kilograms). Their wingspan is 5.6 feet (170 centimeters).

These birds have compact bodies with long necks and full webbing between the three forward-pointing toes. The lower bill is flat while the upper is cone-shaped with a sort of nail at the tip. Waterfowl are unable to glide but can fly quickly with their necks outstretched. Five species are flightless, including three of the four species of steamer-ducks, the Auckland Island teal, and the Campbell Island teal. Screamers look like geese but they have a small, chicken-like head. Their feathers are gray or greenish-black, with some white on the head and neck, fading into the forewing. The screamer has a feathered "horn" on the front top of its head, and its eyes range from yellow to orange. Screamers, like waterfowl, have webbing between their toes.

Ducks, swans, and geese have broad wings that come to a point. Feather coloration varies from the white of most swans to the brown of many geese to the bright patterns of many northern ducks. Male coloration is more vibrant than that of females. Geese and swans molt, shed their feathers, once a year while ducks molt twice each year. During the molting season, waterfowl are flightless except for the magpie goose. Screamers molt gradually and so are never rendered flightless.