Preening (bird)

Preening is a maintenance behaviour found in birds that involves the use of the bill to position their feathers, interlock barbs that have become separated, clean and keep ectoparasites under check.

Because feathers are critical to a bird's survival — contributing as they do to insulation, waterproofing and aerodynamic flight — birds spend a great deal of time maintaining them. For example, one study found that gulls spend 15% of their daylight hours preening during the breeding season. Preening can be associated with and follow or precede other maintenance behaviours including dusting, bathing, sunning, oiling or anting. Although preening is primarily an individual behaviour, some species indulge in allopreening, with one individual preening another, especially in hard to reach locations. The action of allopreening and its solicitation play roles in establishing hierarchies and in forming bonds within social groups of birds.

Preening may involve two kinds of bill actions - nibbling (or mandibulating) while working the feather from base to tip and secondly stroking, either with the bill closed or open. In grebes this is done more vigorously with an open bill and is termed as stropping. In penguins, the head is also used in a motion referred to as wiping. Some birds will also use their feet in an action termed as scratch-preening which is usually applied to the head. Some species (including nightjars, herons, frigatebirds, owls and pratincoles) have comb like serrations on the claw (a pectinate claw) of the middle toe which may aid in scratch preening. While some species use the leg over the lowered head while the wing is held low, others extend the leg between the wing and the body.

Many birds have a preen- or uropygial gland opening above the base of the tail feathers. This gland produces a lipid rich secretion that is applied first to the bill and then to the feathers. The preen-gland is absent in the ratites (emu, ostrich, cassowary) as well as some neognath birds, including bustards, a few parrots and pigeons. The gland is large in aquatic birds. The uropygial secretion plays a role in reducing the growth of fungi and bacteria. In some cases such as hoopoes there are symbiotic Enterococcus faecalis that prevent the growth of harmful bacteria such as Bacillus licheniformis. During moult, the pinfeathers have sheaths that need to be removed during preening as the feather emerges. Some birds like the herons have special feathers called powder down which breakdown into a fine dust which the birds apply to their contour feathers while preening.

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