The birds are a unique group of vertebrates.

There are about 8500 known species in the world, all belonging to the class Aves. Thev are considered to have evolved ■F

about 1 50 million years ago from the thickly feathered Archaeopteryx, which links reptiles to birds. Birds and reptiles have much in common, such as the ability to lay eggs, but no other class of animal has feathers. The possession of feathers, and in the majority of species the ability to Hy. is the reason for their success. I-Iight allows them Iocolonisc new habitats, find new sources of food and to escape predators. Much of their anatomy and physiology has evolved to facilitate life in the air.