Preening.
Preening is a bird maintenance behaviour that involves using the beak to position feathers, interlock the barbules, clean plumage, and reduce parasites. Feathers contribute to a bird's insulation, waterproofing and flight, so birds spend much time on preening. They may fluff up their feathers to "rezip" the barbules, and use their beaks to gather preen oil from a gland at the base of their tail. They spread the oil by drawing each contour feather through their bills. Ritualised preening has become part of some courtship displays and a displacement activity when birds are subjected to stress. Preening can be a social activity involving two or more birds called "allopreening", which occurs either between a mated pair or flock members in a social species. This may assist in grooming, the recognition of individuals, or reducing conflict. Most allopreening is confined to the head and neck. Ingestion of pollutants or pathogens during preening can lead to health problems. Injury and infection can cause overpreening in caged birds.
