Our perception of birds is associated with expanses where feathered predators soar high in the sky or flocks of geese and cranes fly one after another. We know how mobile birds are, how fast and agile they are in flight. They fly over great distances, crossing seas, mountains and deserts during the migration season. Flying from one continent to another as the seasons change, the birds are active all year round.
The ability of the avifauna to fly gives it an advantage over many other animals. They owe it to the physiological structure of their elongated body with the primary and covert wing feathers that form a dense surface area that supports the bird in the air. Birds lift their wings using the strong muscles attached to an inactive thorax. The bones of birds are very difficult to break and strong, as they contain more mineral salts. However, the skeleton of birds is very lightweight, because many bones are hollow and filled with air. Birds are warm-blooded, constant and high temperature (40-42 °C) allows them to fly in the high cold layers of air and enable them to live in a wide variety of climatic niches. Higher metabolic rates in birds make their heart work hard, and indeed birds have a much greater number of heartbeats than mammals, and small birds have the higher heart rate than large ones.