Preening is a maintenance behaviour found in pigeons that involves the use of the beak to position feathers, interlock feather barbules that have become separated, clean plumage, and keep ectoparasites in check. Feathers contribute significantly to a pigeon's insulation, waterproofing and aerodynamic flight, and so are vital to its survival. Because of this, pigeons spend considerable time each day maintaining their feathers, primarily through preening. Several actions make up preening behaviour. Pigeons fluff up and shake their feathers, which helps to "rezip" feather barbules that have become unhooked. Using their beaks, they gather preen oil from a gland at the base of their tail and distribute this oil through their feathers. They draw each contour feather through their bill, nibbling it from base to tip.