Debbie Smith, age 12, of Livingston. N. J.,, for her question:
What exactly are feathers?
A bird is one of the best-dressed animals in the whole world. His coat is soft and Very waxen. It sheds the rain. The stiff pinions in his wings and tail beat the air and use it to lift the bird above the ground. Only a bird is clothed in feathers. Yet his feathers are related to the glassy scales of a fish, to the woolly fleece of a sheep and even to the hair on your head.
Feathers are made of dead, cornified cells, very much like the cells that form your nails and hair. They grow from special buds in the epidermis or under skin of the bird. The scales of fishes and reptiles also grow from special roots in the skin and so do the wool and hairy fur of the mammals. A feather, however, is more elaborate than a scale or a hair. What's more, a bird has several different types of feathers.
His streamlined body is covered with overlapping contour feathers. His wings and tail are set with yaws of stiff, strong pinion feathers. If he is a duck, he has an undercoat of downy feathers. Each of these different feathers has a central shaft, somewhat like the middle vein of a leaf. The quill tip of the shaft is set deep in the skin, and the bird has surface muscles to Move it. He can ruffle his feathers ox make them lie flat.
On each side of the shaft, there is a raw of barbs, like fine silken threads. The barbs form the flat, leafy vein of the feather. Each barb has several hundred flat branches called barbules, and the barbules sprout tiny booklets. These thorny little snags hold the silken barbs ciose together and also interlock the overlapping contour feathers.
The downy feathers, which cover a fluffy chick, have very short shafts. The silken barbs seem to grow from a small spot in the skin. These barbs are soft and loose, and they have few hooks and burbles to hold them together. Some contour feathers have barbs of this type at the base of the shaft. The barbs at the tip and center of the feather form a stiff ribbon to shut out the cold and shed the rain. The downy barbs at the base of the shaft form a warm coat under the overlapping tips of thee contour feathers.
A bird preens his wonderful feathers several times each day. He holds and gently draws them through his bill, from the base to the tip. This smoothes the tangled barbs and flattens the ruffled pinions into stiff ribbons. The preening also adds oily brilliantine, which helps the smooth, well groomed feathers to shed the rain. In time, each feather graves old and worn. It falls out, and a new one grows in to replace it.