Creature Comforts

By Peter Ryan

To care for their plumage, birds undertake a range of activities. Feathers are dead structures that need constant attention to function effectively for flight and insulation. Birds replace their feathers regularly, but this is a costly process, so they spend considerable effort to ensure their feathers remain in good shape for as long as possible.

PREENING

The most obvious of these comfort behaviours is preening, where a bird uses its bill to groom its feathers and skin. Typically, the bill nibbles along the length of each feather from base to tip. This has several functions. First, it cleans feathers of dust and external parasites. Second, coupled with stretching and shaking, preening ensures feathers are aligned correctly.  And thirdly, it repairs any breaks in a feathers vane by reconnecting its inter-locking hooks, like sealing a zip-lock bag. In most birds, preening also serves to spread the oil from the uropygial or “preen” glands over the feathers, skin, legs and bill. A preening bird repeatedly rubs its bill and head over these glands, located at the base of the tail. This coats the bill and head with a thin film of oil, which is then transferred to the rest of the body. Preen oil helps to maintain feather integrity and flexibility, as well as enhancing waterproofing. As a result, preen glands are well developed in most waterbirds. But not cormorants and darters, which have partially or fully wettable feathers to reduce their buoyancy when diving. Preen oil might also help to deter lice, mites and other feather parasites. Birds that have a large diversity of parasites tend to have large preen glands. In a few groups, such as hoopoes and wood-hoopoes, symbiotic bacteria live in the preen gland, making the preen oil particularly pungent. Their presence gives the oil anti-bacterial properties. Which help slow feather degradation. They also make the birds distasteful to mammals such as genets, which probably helps to reduce the risk of predation while roosting in tree cavities.

DUSTING

All birds have preen glands as chicks, but they cease functioning as birds develop in groups such as the ratites (walking birds – Ed.) and bustards. These birds typically use dust to help keep their feathers clean, although this behaviour is by no-means-confined to birds without preen glands. Dusting is common in ground-dwelling birds, especially in arid areas where water is scarce, limiting the options to bathe. Among Southern African birds, it is particularly common in gamebirds, larks and sparrows. A more sophisticated approach is to grow your own “dust”. Herons and some parrots have special powder down feathers that are unique in continuing to grow year round.

ANTING

This is either done indirectly, by lying with wings and tail spread where ants are active and quivering to encourage them to “attack” the bird, or directly, by rubbing ants over the flight feathers. In most instances of direct anting, the ants are discarded after being wiped over the plumage, but some birds do eat them.

SCRATCHING

Birds cant reach all parts of their bodies with their bills, so inaccessible parts such as the head, throat and bill are groomed with the feet in ritualised scratching behaviour. In the extreme case of the sword-billed hummingbird, its bill is longer than its body, rendering it virtually useless for preening, so all grooming is done by the feet.

BATHING

Preening may occur at any time, but it is often associated with bathing. The actual process of bathing varies among birds, from wetting their bills while preening, through standing in water, to swimming and even plunging into water from the air. Some birds also bathe in the rain, or use dew on leaves and other vegetation. Bathing usually is accompanied by vigorous shaking and ruffling of the feathers, and typically is followed by a period of extended preening.

SUNNING

To care for their plumage, birds expose themselves to the heat of the sun on hot days, fluffing up their body feathers and spreading their wings. In vultures, this has been shown to help restore flight feathers to their original shape if they become stressed in flight.

SOCIALIZING

From a human perspective, perhaps the most interesting aspect of comfort behaviours is their use in social context. Birds often preen each other, recalling human couples canoodling. This allopreening does indeed serve to help establish and maintain pair bonds, or social cohesion among group-living birds. It is concentrated on the head area, where birds cant preen themselves with their bills.

Wild Magazine Autumn 2013