INTRODUCTION

                     Birds are ‘warm-blooded’ vertebrates, with fore-limbs modified to wings, and skins covered with feathers. Vertebrates are characterised by having a spinal column and a skull. ‘Warm blooded’ or homoiothermic (constant temperature) means that their body temperature is kept more or less constant and above that of their surroundings. Typically, the forelimbs as wings give birds the power of flight although there are some flightless birds. In some cases (e.g. penguins and puffins) the wings are used for swimming under water.

All birds reproduce by laying eggs which are fertilised internally before laying.

The skull and lower jaw are extended forward into mandibles which make a beak.

The bird's legs and toes are covered with overlapping scales.

Birds possess a third, transparent eyelid, the nictitating membrane, which can move across the eye.