Birds are feathered bipeds. They belong to class Aves and subphylum Vertebrata. The most distinguishing character of birds is the possession of feathers and the forelimbs modified into wings. Birds descended 140 million years ago from the reptilian stock similar to that which produced dinosaurs, a bird-like creature, called Archaeopteryx.
General characteristics of bird
- Body covered by feather, air-breathing, warm-blooded, egg laying and bipedal flying vertebrates.
- Body is more or less spindle-shaped and divisible into head, neck, trunk and tail. Head bears jaw bones prolonged into a toothless beak. Neck is long and flexible. Trunk is compact and tail is short and stumpy for balancing, steering and lift during flight.
- They have one pair of legs and one pair of wings. Legs are large and are adapted for walking, running, scratching, perching, capturing food, swimming etc.
- Wing bears three clawless digits and leg bears four clawed toes, of which the first or hallus is directed backwards.
- Body is covered with feathers forming a non-conducting body covering for warmth and lightness of bodyweight.
- The bones of birds are different to those of other animals. They have a hollow space inside the bone filled with air, which makes the body light so that birds can fly easily.
- Gullet dilated into a crop for quick feeding and storage. Stomach is divided into a glandular proventriculus and a muscular gizzard.
- Heart is four chambered.
- Lungs are spongy and non-distensible. Air-sacs are present and some of them communicate with air cavities in the bones.
- Vocal cord is absent in birds but they produce sound with the help of sound box (syrinx) present at or near the junction of trachea and bronchi.
- Parental care is highly developed, ensuring safety of the eggs and young.