Point out that the hollow bones reduce weight. Struts in some of the bones help strengthen the bones without adding much extra weight. How Birds Fly Like airplanes, birds are streamlined and are built of light materials so that they can lift easily in the air. Feathers point backward. Bills are lighter and more streamlined than the heavy jaws of mammals and reptiles.
Most bird bones are hollow and filled with air from the bird's lungs.
Even the wishbone is hollow. Next time you eat chicken or duck, look at the hollow bones. Birds move through the air by pulling themselves forward like a person rowing a boat. They push air down and back with the broad side of the wing, then slightly turn and fold the wing to move it forward. Some birds with great, broad wings can soar and glide for long periods without flapping.