Feathers are unique to birds: all birds and only birds have them. They evolved from the scales of birds' reptilian ancestors. Feathers are made of keratin, just like your hair and fingernails, and are lightweight, yet strong.

The hard central shaft of a feather is the rachis. Parallel rows of barbs make up the feather vane.
In turn, several hundred tiny barbules branch off from each barb. These overlap with barbules from the neighboring barbs.
The barbules on the outer side of the barb have microscopic hooklets to help interlock the barbs, like velcro, and hold the vane together.

Because feathers are critical for flight and insulation, birds keep them well-maintained. A good portion of a bird's day is spent cleaning and grooming its feathers by applying oil, bathing in water or dust, scratching, and preening. Preening straightens out the barbs so they lock neatly together. The preened feather presents a solid surface to push against air during flight.

The uropygial gland, or preen gland, secretes an oil birds use to groom and waterproof their feathers. Birds obtain the oil with their bills and spread it over their feathers.

Birds replace old feathers with new ones in a process called molting. Molting occurs one or more times a year. It takes a lot of energy to grow new feathers, so molting usually does not coincide with other annual events that require a large energy investment, such as migration or rearing young.

During molt, feathers are usually replaced in an orderly, predictable sequence. This is especially true of wing and tail feathers, where symmetry must be maintained for balanced flight.

Look at the skin of a chicken or turkey before it is cooked. Notice the "goose bumps)" Each bump is where a feather was attached. Notice how the bumps, or feather follicles, are arranged in precise patterns or "feather tracts." Different kinds of birds have different patterns of feather tracts.

Each feather may have 40 or more tiny muscles attached to its base. Birds raise and lower feathers during courtship displays and to control body temperature. Have you ever seen a puffed-up sparrow in winter! Its fluffed feathers offer insulation, like a thick sweater.

Classroom Activities: Hooked on Feathers Keeping Warm