Birds are warm-blooded, egg-laying, feathered vertebrates. They are members of the class Aves. Their
forelimbs are modified to form wings, though not all birds can fly.
All birds have feathers. Feathers are highly modified versions of scales that covered anscestral birds. The form of the scales has changed over millions of years to do different kinds of jobs. Birds have several different types of feathers.
Contour feathers, which grow on the body, wings and tail, are designed to direct air flow around the bird so it can get into the air and control its movement during flight. Some contour feathers on the wings and tail are especially designed as flight feathers and act as flight control surfaces, providing lift and allowing the bird to perform very precise movements during flight.
Down feathers, which grow close to the bird's skin under the contour feathers, help control the bird's body temperature. Some types of down feathers disintegrate to create a powder that helps make the feathers of water birds waterproof.
Semiplumes, which also grow under the contour feathers, help to insulate the bird and contribute to a smooth, aerodynamic body shape.
Filoplumes, which are mixed in with all the other feathers covering the bird, are attached to nerves that give the bird a sense of touch all over its body, even though it is covered with feathers that do not transmit much sensation.
Bristles are short, hairlike feathers that are attached to sensory nerves. Not all birds have them. They usually grow around the eyes and mouths of certain species of birds. They are very sensitive to touch and the birds use them the same way a cat uses its whiskers.
Birds eat a variety of foods including: insects, worms, fish, small mammals, reptiles, and amphibians, fruits, nuts, grains, and nectar. Many birds specialize in a type of food. Hawaiian Honeycreepers, such as the rare 'I'iwi, for example, eat nectar from the flowers of trees.
