Semiplume Bird Feathers

In appearance, semiplumes fall between contour feathers and down feathers, combining a large rachis with downy vanes. Semiplumes are distinguished from down feathers in that the rachis is longer than the longest barbs. They fill in or smooth out the various contours of a bird's body while insulating it, and they also provide flexibility at constricted areas, such as the base of the wings. Semiplumes are usually hidden beneath the contour feathers and are small and often white.