Flying
Birds fly higher, farther and faster than any other flying animals. Many species can span entire oceans and continents on their migrations. Birds are also the only flying animals that regularly use the wind as a source of lift. A bird’s wings are powered by two sets of muscles on the breast. In most birds, these muscles make up about one-third of their total weight. Muscle powers move the long, stiff flight feathers. Feathers at the wind tips, called primaries, propel the bird forward, while the rest of the wind generates the lift. The wings change shape as they beat up and down. They are broad and extended on the down stroke, but tucked in tight on the upstroke. Wings shape and how a bird lives are closely related.. Long wings are more efficient than short wings, but much harder to flap. Birds with long wings are usually soaring birds. Short-winged birds have less stamina, but can build up speed very quickly.