Birds evolved about 200 million year ago in the form of crow-like animal called ‘Archaeopteryx’ that is found in the form of fossils now.

Birds vary in forms and size. The smallest one may be smaller than the butterflies or moths and weighs about 1.5 gram. It is found in North Africa. Birds are distributed all over the world from equator to poles. Presently more than 8500 species of birds are found the world over. Birds are capable of flying but some species have lost this property. They maintain their body temperature at 110 F. They have very light skeleton and require 15 times more energy for flying then normal activities.

Except beak and claws, body of birds is covered with feathers. Feathers vary in size and shape and help the animal to maintain its body temperature. Shapes of the feathers ensure different flight characteristics.