Feathers are the outer covering of a bird. They have a shaft which is the stiff rod between the soft vanes. The vanes consist of tiny barbs which interlock to keep the individual branches together. On each barb, there is an even smaller system of barbules and hooklets which keeps the barbs together. When a bird preens, or adjusts its feathers with its beak, often it is repositioning these barbs and hooks back into their respective places.