barbule

Barbule is a small filament that extends from a feather barb in birds. Each feather vane is composed of barbs, and from each barb project numerous barbules. In many pennaceous feathers, the barbules bear tiny hooklets, or barbicels, at their distal ends that interlock with neighboring barbules to form a cohesive, continuous surface.

Structure and variation: Barbules can be proximal or distal along a barb, and their density and hooklet arrangement vary by species and feather type. In flight feathers, interlocking barbules create a smooth, rigid vane, whereas in downy plumulaceous feathers the barbules are sparser and less interlocked, producing a fluffy texture that traps air.

Function: The interlocking barbules maintain the integrity of the feather surface during flight and help reduce drag, while other properties such as waterproofing are enhanced by preen oil spread by the uropygial gland and by the microstructure of the barbules. Damage or wear to barbules can compromise flight, insulation, and waterproofing.

Development and distribution: Barbules are present on most pennaceous feathers of adult birds. Their specialization varies with ecological needs, such as aquatic life requiring strong interlocking and waterproofing, or species with different aerodynamic demands.

Research and applications: The microstructure of barbules is studied with microscopy, and its hydrophobic and mechanical properties have inspired biomimetic materials and textiles.