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.