There are about 9000 living bird species. Birds are from the diverse class called Aves. It was generally believed that they evolved from reptilian dinosaurs. Read on to learn more about the unique characteristics of birds:
Feathers are the defining characteristic of Aves, found on every living species of bird and no other class of animal. Feathers are made of keratin, the same substance that forms hair and nails in other animals and are highly modified scales. Feathers are critical not only for flight but also for warmth and protection against the elements — and in many species, for males to attract mates. Soft, fluffy downy feathers help keep birds warm, contour feathers streamline birds’ bodies and aid in flying, and flight feathers on wings and tail give the bird loft. Birds shed, or molt, old feathers once or twice each year, depending on the species.
All birds have wings, although not all birds fly. Nor are wings confined to Aves; bats are flying mammals and most insects have wings. Birds’ bodies are beautifully designed for flight, with strong chest muscles and just enough curve to their wings to provide lift. Differences in wing shape provide different advantages to the various bird species. The narrow, sharp-tipped wings of the falcon provide speed; albatrosses soar high on wings much longer than they are wide. Most songbirds have elliptical, evenly shaped wings that facilitate quick, small movements in the tight spaces of their tree homes. Swimming birds, such as penguins and puffins, have flipper-shaped wings that propel them rapidly and gracefully through water.