The vane is held together by thousands of tiny barbs. A bird must preen its feathers often in order to stay warm and dry, and in order to fly. Flight feathers are the long feathers on the wings and tail used in flying. Wing flight feathers can be easily identified because the shaft does not divide the vane evenly. Down feathers are the small fluffy feathers found under the contour feathers.
Birds use their down to keep warm, too.
Sometimes birds fluff up their feathers which makes them look fat. Birds do this to create air spaces between the feathers. These spaces hold air heated by the body which provides insulation from the cold. After-feathers are small feathers that emerge from the same shaft as a contour feather. Best seen on grouse and ptarmigan, after-feathers help insulate the bird and fill out body contours.