“The Birder’s Handbook” (Ehrlich, Dobkin, and Wheye) states “Birds are defined by feathers—no bird lacks them, no other animal possesses them.”
Feathers are very important to birds. They make flight possible. They provide insulation and protection from the cold and the heat. They protect from sunburn and rainfall.
Woodpeckers have strong, pointed tail feathers that they use to prop themselves up while they whack at a tree. Colorful feathers are used by some birds for display. Drab feathers help to provide camouflage. The authors conclude “Feathers not only define the bird but are essential to its existence.”
Birds have different feather types on their body, head, wings and tail. They’re all made of beta-keratin, the same protein that’s in their beak and claws, and our hair and fingernails. Here are the most common types of feathers.
Flight feather: The tube that goes up the entire flight feather is called the rachis. It’s centered in most feather types, but it’s offset in the flight feather. The little vanes that come out from the rachis are shorter on the leading edge of the feather. This design lets one feather overlap the next forming a seamless, aerodynamic wing, that also sheds rain. In addition, the vanes have tiny hooks and ridges that keep each feather in proper shape for flight. The bird can simply run its beak along the feather to zip up the hooks and ridges again.
Contour feather: Contour feathers are the body feathers that shape the bird. House sparrows have about 1,800 feathers in the summer, about 1,400 of them are contour feathers. Contour feathers are symmetrical with vanes of equal length on each side of the rachis. There are no contour feathers on the wings or the tail.
Semiplume: Semiplumes have a central rachis, but the vanes are frilly and not interlocked. These feathers help to provide insulation between the contour feathers and the down feathers.
Down feather: The down feather doesn’t have a rachis; the vanes or plumes emanate right from the rim of the quill or calamus at the bottom of the feather. The plumes are elongated, not interlocking. Their fluffiness provides insulation by creating air pockets.
Bristles: A bristle is essentially a stiff rachis with no or few vanes. Bristles serve as sensors or in a protective capacity, for example, protecting the bird’s eyes from incoming bugs.
Filoplume: The filoplumes act like little wind gauges surrounding each flight feather. They don’t have any muscles in the socket, unlike the other feathers listed above, but their movement is reported to the bird’s central nervous system and helps the bird take off, fly, land, and maneuver.
Powder down feathers: Most birds have a preen gland above the base of the tail which secretes an oil that the bird uses to groom its feathers.
But some birds such as pigeons, hawks, herons, bitterns and parrots don’t have that gland. They have what are known as powder down feathers, that break down into fine powder the bird uses for grooming and waterproofing its feathers. The powder down feathers are concentrated in dense patches in herons, for example, but scattered in hawks. Sounds like a serious dandruff problem.
Summary: Now that we’ve described several different kinds of feathers, let’s stick them onto an imaginary bird to see where they go and what they do.
If we start with a naked bird, we’d first add a layer of down feathers on the body. This is the thermal underwear that keeps birds cozy when it’s chilly. But it’s not very effective if it gets wet. That’s why the down layer must be protected by the contour feathers.
The contour feathers, also on the body, interlock and form a waterproof layer above the down feathers. Any rain is shed off without dampening the down. Wind doesn’t get through the contour feathers, either.
Between the contour feathers and the down feathers are the semiplume feathers. They’re like a frilly contour feather that’s got some downiness to it. They help improve the insulation of the down layer.
The flight feathers are on the wings, of course. These are the feathers that are asymmetrical with longer vanes on one side of the rachis. That allows the feathers to overlap with their neighbors, producing a strong aerodynamic instrument for flight.
Filoplumes surround the base of each flight feather. They send signals that move or rotate each flight feather while in flight.
Not all birds have bristles, but those that do are most likely using them to protect their eyes from incoming bugs.
And the powder down feathers are used by some birds as a source of preening powder. Not really dandruff at all.
So, the next time you find a feather on your walk you can now additionally impress your friends and family by identifying its type and purpose.
Clay Christensen lives and writes in Lauderdale, Minnesota.