Down and Powder Down Bird Feathers

Down feathers make up the underplumage of a bird. They are usually concealed beneath the contour feathers, and their main function appears to be insulation against the cold weather. Each down feather has a quill and a soft head of fluffy barbs, but there are no barbules and the barbs are not "zipped" together as they are in contour feathers. These feathers are especially numerous in ducks and other water birds. In some species of water birds the adults pluck down feathers from their beasts and use them to line the nest and keep the eggs warm. Chicks of some species are covered with down when they hatch.

Powder down feathers help insulate the bird. Unlike other feathers, powder downs grow continuously. Instead of being molted, their tips disintegrate into a powdery substance. These feathers grow in dense, yellowish patches on the breast, belly, or flanks of herons and bitterns. In other birds powder down feathers are more thinly scattered throughout the plumage. Many ornithologists believe that in water birds the powder serves to soak up water, blood, and slime, thus protecting the feathers and making preening easier.