Generally five types of feathers cover the body of a bird: contour, semiplume, down, filoplume and bristle. Contour feathers are the feathers that cover and protect the bird. They are sort of staggered like scales on a snake. The most common contour feathers that people find on the ground are the tail and flight feathers. At first look they may seem the same, but tail feathers are usually more balanced with a stiff center shaft and flight feathers have a wider and narrower side to help cut through the air. In between the contour feathers are semiplumes that provide both support and insulation. Underneath the contour feathers are down feathers. The purpose of down feathers is to trap air between the feathers and the bird’s skin to insulate it. Some birds, such as baby chicks, are born covered in down.
Other feathers act as sensors. Filoplumes are bare except for a few barbs. They grow around contour feathers and may help birds sense the position of feathers in flight. Bristle feathers look like little stiff hairs and grow around some birds’ beaks or eyes. Bristles may help birds such as swallows catch prey by funneling insects toward the mouth. They may also protect the eyes. Woodpeckers have bristles over their nostrils that help keep wood chips out. Bristles may also act like a cat’s whiskers helping a bird feel what’s around it.
Because feathers are critical for flight and insulation, birds keep them well-maintained, especially in the winter. After a bath the birds obtain oil from the uropygial gland and reapply it with their bills to straighten and waterproof their feathers.
Some birds that don't have the preen gland like pigeons and herons also grow powder down feathers. These feathers grow continuously and never molt. Instead the barbs at their tips constantly disintegrate into a fine, talc-like, water-resistant powder.
Why Birds don't Freeze After They Take a Bath in the Winter: http://bit.ly/mPa0Y8
How small birds stay warm in the winter: http://bit.ly/q3dDqj
Bald bird: http://bit.ly/nmAoXV
Why birds molt: http://bit.ly/ox5HwiBlue Jays aren't blue: http://bit.ly/pMN37k
Fossils of colored feathers: http://bit.ly/nc2UeA
Feather photo: http://commons.wikimedia.org/wiki/File:Parts_of_feather.jpgFeather Structure: http://www.birds.cornell.edu/AllAboutBirds/studying/feathers/feathers
Clipart courtesy FCIT http://etc.usf.edu/clipart