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: Head
Scratching;
Anting;
Disease
and Parasitism. Copyright
® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl
Wheye.