BIRDS AND BUTTERFLIES
Only Birds Have Feathers
By Julie Jansen
Feathers are the ultimate characteristic of birds. No other(living) animals have them. The qualifier is required because feathers have now been found in fossil imprints of some dinosaurs and related reptiles. Like hair on mammals and scales on reptiles, feathers are part of the skin. All are largely composed of keratin, which is also the main ingredient of human nails, animal claws, and the scales on the legs and feet of birds.
Feathers are remarkable structures, both very strong and very light. They're subject to long flights and are bent and twisted, yet they are rarely damaged. Abrasion causes their tips and edges to wear, but this is natural and remedied periodically through molt. Melanins are common pigments that can make feathers black. Dark feathers containing melanins are more resistant to damage than other feathers. This is why the outer wing feathers of many birds with white wings, such as gulls and snow geese, have black tips. Birds have several different feather types that vary in shape, structure, and function. The most familiar is the contour feather. It consists of a central shaft and countless barbs that protrude from either side, forming vanes. Vanes of contour feathers must be rigid and flexible at the same time. A magnifying glass reveals that eachbarb has smaller barbs, called barbules, projecting from either side, toward the adjacent barbs. The barbuleson one side of the barb are straight, while those on the other are hooked. If barbs separate and the vane split,the bird can repair it by preening. Running the barbs through its bill reconnects the hooks like a zipper.Strong, rigid vanes are especially important for flight. The trailing, inner wing feathers, the secondaries, provide lift, while the trailing, outer wing feathers, the primaries, provide thrust. Most species have large tail feathers. They function like a rudder when flying and like brakes when landing.
Smaller contour feathers cover the body and leading edges of the wings. On the wings, the feathers help form the airfoil shape that is necessary for flight. On the body, they contribute color, which is important in courtship and for camouflage, and they form a sleek outer covering, providing an aerodynamic tear-drop shape that assists flight. From songbirds to swans, the neck is narrow and the breast muscles are massive. Where the body parts meet, contour feathers create a gradual slope.
Another type, down feathers lie under the body's contour feathers, forming a mass of feathers that trap air, forming an excellent layer of insulation.
Other types are quite specialized. They are associated with sensory receptors in the skin, and are thought to provide information about wind, air pressure, and feather movements that birds use to maintain efficient flight. Feathers are highly engineered structures that perform essential functions. Lightweight and strong, they allow birds to be amazing creatures.