Bathing and Dusting

painting of a Violet-green Swallow by Carel Brest van Kempen
When birds bathe in water or saturate themselves with dust they are actively maintaining their plumage. In well-watered areas bathing is most common, in arid ones dusting is more often observed. Experiments with quail show that frequent dusting helps to maintain an optimum amount of oil on the feathers. Excess plumage lipids, including preen oil, are absorbed by the dust and expelled along with dry skin and other debris. If quail are prevented from dusting, their feathers quickly become oily and matted. Dusting may also help to discourage bird lice, but no experimental evidence exists as yet showing that to be the case.

Wrens and House Sparrows frequently follow a water bath with a dust bath (one reason to suspect an anti-parasite function for dusting). Overall, the amount of time and effort birds put into bathing and dusting indicates how critical feather maintenance may be. Feathers are marvelous and intricate devices, but keeping them functional requires constant care.

A bird is considered to be bathing whenever it uses any of several stereotyped movements to wet its feathers. One pattern, wading, is commonly observed in birds with strong feet and broad, short, flexible wings. In a typical sequence a bird stands in the water, fluffs the feathers to expose the bare skin between their bases, and rapidly flicks the wings in and out of the water. The breast is submerged and rolled vigorously back and forth, and then, as the front end emerges, the head is thrown back, forming a cup with the partially elevated wings and tail, and dousing the feathers of the back. Those feathers are elevated so that the water reaches the skin, and then lowered, forcing the water between them. The sequence may be repeated, with the bird submerging farther in each cycle, until it is a mass of soaked disarranged feathers. Variations on this theme can be seen in different species, such as robins, thrushes, mockingbirds, jays, and titmice.

Birds with weak feet, such as swifts and swallows, which spend most of their time flying, dip into the water in flight, thus getting their baths "on the wing." As the body is dipped, the tail is raised to direct a spray of water over the back, and the feathers are vibrated. Flycatchers dive repeatedly from their perches into water, and vireos, which may combine both wading and diving, stand briefly and dip in the water between dives.

Chickadees, yellowthroats, wrens, buntings, and waterthrushes dart in and out of water, immersing and rolling briefly, before returning to shore to flick their wings and vibrate their feathers before jumping in again. The Wrentit, which often lives in habitats where pools of water are scarce, wets its plumage with dew from vegetation.

For birds with stubby, weak legs not adapted to wading, bathing is passive. Most woodpeckers and nuthatches, for example, simply expose their feathers when it is drizzling. They have characteristic bathing postures, extending their wings and spreading their tails.

The frequency of bathing by land birds typically is related to the weather. On a hot summer day titmice or chickadees may take five baths; in midwinter they still may bathe several times a week, often in snowmelt found in protected areas.

Waterbirds and seabirds also bathe with stereotyped routines. Terns that spend most of their time flying bathe in the same way as swifts. Grebes, ducks, geese, and swans bathe either on the surface or while diving, opening their feathers and wings. Gulls and some rails bathe while wading.

After bathing, birds dry themselves using ritualized movements. Even swimming birds must force the surplus water from between their feathers to protect their insulating properties. Anhingas and cormorants, which often sit in a characteristic sunbathing posture with drying wings spread, are perhaps also thermoregulating. (Vultures take on similar sunbathing postures in the morning. Sunbathing, which occurs in many birds, may stimulate skin parasites into activity so they can be more readily picked off.) Songbirds shake themselves to throw off water by vibrating wings and tail and ruffling feathers. All birds normally follow bathing with preening.

For some species that live in areas where standing water is not readily available, dusting appears to substitute for water bathing. Birds create dust wallows by scraping the ground. They throw dust over their bodies and rub their heads in the wallow. The dust is first worked through the feathers and then shaken out. Wrens, House Sparrows, Wrentits, larks, game birds, and some raptors are among the North American birds known to dust. As with water bathing, different species tend to have somewhat different dusting routines.

SEE: Temperature Regulation and Behavior; Head scratching.
Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.