One adaptation birds have for flight are their wings. To get power for flight, birds must flap their wings by contracting their large breast muscles, which are anchored to a keel on their sternum. Many birds use the air currents to soar and glide, while other species must continuously flap their wings to hover. However, not all birds fly. Some birds have evolved to be flightless in the absence of predators or to enable them to swim, which is the case for penguins, states Birds in Backyards. Also, a bird's body temperature is around 104 degrees Fahrenheit, which is higher than the temperature of an average mammal, according to Birds in Backyard. This is due to their insulating feathers and a layer of fat that can be found in certain species. Their higher body temperature allows the cells in their muscles to work 2.2 times faster, and as a result, allows their muscles to relax more rapidly, explains Birds in Backyards.
If a bird is just gliding (or "soaring"), that is, not flapping its wings, it flies in pretty much the same way that an airplane flies. The wings push air down, so by Newton's third law the air must push them up. Partly, the push comes from the angle the wings are held at and partly from the curvature of the wings. The air travels faster above the bird's wing than it does below, and this makes the pressure lower above the wing. Here's a about such airfoils.
Let’s talk about aerodynamics (air-oh-die-NAM-icks). That’s the science of how air moves around things. It helps explain how birds fly. A bird uses its legs to push off the ground into the air. That’s called thrust. It flaps its wings to stay in the air. That’s called lift. When you put thrust and lift together, a bird flies. Its wings also have a curved shape, like an upside-down spoon. This shape helps the air move above and below the wings and keep the bird in the air. Birds’ feathers also help them fly. Air rushes through the feathers, creating more lift.
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