INTRODUCTION

When we pay a visit to a zoo or park or wildlife Sanctuary the group of organisms which fascinate us are ‘Birds’. Why are we attracted by them so much? It is because they are among the most colourfull and musical creatures inhabiting the Earth.

Birds occur in every habitat from polar ice to tropical deserts. Some have also adopted to live in water. Birds started to flight some 150 million years ago.

This class includes the vertebrates which are adopted for aerial or volant mode of life. Birds are one of the most fascinating and widely known animals distributed all over the world. More than 8,600 species of birds are known.

Birds share with mammals the rank of the highest vertebrates .In many respects birds are the most highly specialized of craniata.They show perfect adaptation for aerial life and almost every part of their organization is modified. This include non-conducting covering of feathers, the modification of the forelimbs as wings of the sternum and shoulder girdle to serve as origins of the wing muscles and of the pelvic girdle and hind limbs to enable them to support the weight of the body. The respiratory system is also perfected for aerial modification.

Some other characteristic features include the absence of teeth, the loss of left aortic arch and right ovary and oviduct, the specialized character of the brain, the poorly developed olfactory organs and large and perfect eyes. All these characters combined together, give a unique place to the group ‘Aves’ in the animal kingdom.