Filoplume Bird Feathers

Filoplumes are always situated beside other feathers. They are simple, hairlike structures that grow in circles around the base of contour or down feathers. They usually stand up like hairs, and are made up of a thin rachis with a few short barbs of barbules at the tip. Filoplumes are generally smaller than semiplumes and are on half to three fourths of the length of the covering contour feathers.

The origins of filoplumes is currently under debate. Some ornithologists disagree with the theory that filoplumes are degenerate contour feathers and believe instead that they are sensitive structures that assist in the nerve endings in the follicle. It is therefore quite possible the filoplumes play a key role in keeping contours in place during preening, display, and flight.