Scanning electron micrograph (SEM) Goose down feather barbules and barbule tips (Canadian goose; Branta canadensis). The feathers on geese or ducks are the outer covering of the bird. They have quills, repel water, and make it possible for the animal to fly. Down feathers lie beneath this protective covering, usually on the belly of a bird. Down feathers (usually called down) are light and fluffy and provides the insulation birds need to keep warm. The loose structure of down feathers traps air, which helps to insulate the bird against heat loss and contributes to the buoyancy of waterbirds. Very young birds are clad only in down feathers. Down is a fine thermal insulator and padding, used in goods such as jackets, bedding pillows and sleeping bags. Magnification: x205 when shortest axis printed at 25 millimetres.
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