This muscle raises the wing after the downbeat, and because this upward movement requires less power, the supercoracoideus is a thinner muscle than the pectoralis. Other major muscles of the bird are found running up the legs, and these are used for running and perching. Unlike other vertebrates, the foot of a bird contains very few muscles, an adaptation that allows the foot to be narrow and streamlined, and prevents heat loss from these unfeathered regions. Wings and flight Birds are unique flying animals because they are the only animals to have a covering of feathers. Groups of feathers on the wings provide the surfaces used to control flight.
Propulsion is provided by the primary feathers, which are the outermost feathers in the wings.
These long, strong feathers push air back and down during the downbeat of the wing. As the wing is pulled upwards again, the placement of the feathers allows air to pass between them, so that drag is reduced. The innermost feathers of the wing are the secondary and tertial feathers. These feathers form an airfoil in cross-section, a curved shape that allows air to move faster over the longer upper surface, providing an upward lifting force. Gliding is the simplest method of flight, relying on the airfoil shape of the wing to generate lift.