Filoplume

Filoplumes are a type of feather found in many bird species. They are characteristically slender and hairlike, with a long shaft and only a few small barbs near the tip. The feather usually projects beyond the surrounding feathers, and its vane is minimal compared with contour or down feathers. Filoplumes develop from specialized follicles and can occur singly or in small clusters on various parts of the body, including the head, neck, wings, and tail.

In contrast to other feather types, filoplumes have little or no vaned surface along most of their length. Their distinguishing feature is the sparse distal barbules at the tip, which gives them a filamentous appearance. This simple structure is paired with a sensory function rather than a primary role in insulation or flight.

The primary function of filoplumes is tactile. They contain nerve endings at their base and act as mechanoreceptors that monitor feather position, movement, and air currents. This sensory input helps birds regulate feather alignment, adjust flight and posture, and respond to changes in wind or body position. Filoplumes may also contribute to peripheral plumage sensing during molt or display in some species.

Distribution and variation of filoplumes vary among birds; some species have numerous filoplumes scattered around the body, while others possess only a few. They are considered a supplementary feather type, distinct from bristles and down, and are valued mainly for their sensory role rather than for insulation or aerodynamics.