[Illustration]
A bird's plumage receives a great deal of care from the bird that wears
it. The bill is the only implement for this grooming, and it is run
through and along the feathers it can reach, helping clean them and
making sure they lie in their proper place in the bird's dress. There
are parts of the plumage that the bird's bill obviously can't reach,
as that of the head, but ducks at least surmount this difficulty by
rubbing their head against their body.
Many birds have oil glands (the only external glands that most birds
have), a pair of glands just above and in front of the root of the
tail, on the back. They contain an oily substance, and the usual
explanation of its use is that the secretion of these glands is used
in dressing the feathers. Certainly birds that have oil glands seem to
use them, nibbling at them as though to press out the oil, touching
them with the bill, and then rubbing the bill through the feathers, and
rubbing the head against the oil gland.
The beautiful, soft, whitish bloom seen on some birds' feathers, such
as the pale gray of a male marsh hawk and filmy appearance of some
herons' plumage, is caused by specialized feathers called "powder
down." Sometimes this powder down is scattered through the plumage;
sometimes it is in patches, such as the particularly conspicuous ones
in the herons. The tips of the powder down are continually breaking off
and sifting over the rest of the plumage, giving it the bloom that with
handling quickly rubs off.
WALNUTS AS A COSMETIC But birds sometimes rub foreign substances over
their feathers--just why we don't know. Grackles have been known to use
the acid juice of green walnuts in preening.
In Pennsylvania starlings have been seen to come to walnut trees when
the nuts were almost three-quarters grown, in June, and peck a hole in
the sticky hull of a nut, clip the bill into it, undoubtedly wetting
the bill against the pulpy interior, and then thrust the bill into
their plumage.
They did this from June to August, especially on hot, dry summer days,
but some birds continued this even during light rain. Some years before
the above was recorded, when this sort of thing was less known, Edward
Howe Forbush, noted ornithologist, cautiously used a similar record in
his classical _Birds of Massachusetts and Other New England States_. He
writes that his colleague, J. N. Baskett, says he saw a bluejay lift
its wing and rub pungent walnut leaves repeatedly into the feathers
beneath.
BEER AND MOTH BALLS Since then such things have been recorded a number
of times, including a catbird that anointed its feathers with a leaf
and a grackle that found a moth ball and, holding this in its bill,
rubbed it against the underside of its spread wing and the side of its
body. After several applications the grackle dropped the moth ball and
preened its feathers; then again it picked up the moth ball and treated
the other wing as well as its belly.
Recent experiments with tame song sparrows have shown that they may use
beer, orange juice, vinegar, and other things made available to them in
dressing their plumage, and it appears that this may be correlated with
a little-understood type of activity known as anting, in which live
ants are placed on the feathers.