Birds are flight orientated organisms. Each part of its anatomy is modified in some way to allow it to keep its body light and energetic for flight.
Very active metabolism. They can eat, digest, and eliminate the waste in a short amount of time. Their body temperature is rather high 102-103 degrees F. They are endotherms.
They contain a four chambered heart.
Their skeleton is constructed of light weight bones supported by an inner meshwork of bony material to give extra support while flying.
The female loses one of its ovaries.
They have no teeth and their beak is made of a light protein keratin.
They contain feathers, also made of keratin. There are three types of feathers: down feathers which are used for insulation, contour feathers which are colorful and used for recognition, and keeping the body aerodynamic, and quill feathers which are used for flight . These feathers are lost periodically (molting).
They have an extensive air sac system attached to the lungs. This reduces the weight of the bird and supplies the needed air for a fast metabolism. It also is used to dissipate the tremendous amount of heat built up from metabolism.
They develop from the amniote egg. Bird egg shells are hardened with calcium carbonate for added protection.
Birds that are ready to carry on life's duties upon hatching are called precotial, while those that need further development are called altricial.
They have a well developed nervous system. Acute vision, and external ears.
Well developed muscles. The keel ,a part of the sternum, allows large pectoral muscles to be attached to the skeleton.
Their forelimbs are modifies as wings. These wings are homologous to the limbs of the reptiles, amphibians, and mammals.
Their hind limbs are modified for various jobs based on the structure of their claws.
Birds are an excellent indicator of the fitness of the environment. They help keep the insect population down, use rodents as a food source, help rid the environment of dead and decaying organic material, and help pollinate many types of plants.
Many birds migrate over long distances to find suitable breeding grounds and protection from major climatic changes.