They are most abundant in the Mississippi Valley. Some island species have lost the power of flight, but most ducks of northern continents are highly migratory. In a few species, the sexes are alike in color, but in most the males are brighter and more boldly patterned. Ducks have elaborate courtship displays, each unique to its species. Nests of most species are on the ground, containing from 4 to 12 eggs, surrounded by down feathers plucked from the female's breast and belly.
Ducklings are able to swim and feed themselves soon after they hatch.
Some species, such as the wood duck, Aix sponsa, of North America, nest in holes in trees, and will accept artificial nest boxes. Their ducklings can jump from their nests without injury, and take to the water soon afterwards. Distances covered by migrating ducks vary with the species. One arctic duck, the spectacled eider, Somateria fischeri, winters at sea off Alaska. Long distance champion among American ducks is the blue-winged teal, Anas discors, which nests in most of North America and winters from the southern United States to Argentina.