This Hawk is soaring through the air in search of prey in the Galapagos islands. The wing clearly functions as an airfoil. The leading edge is thicker than the trailing edge, its upper surface is slightly convex, and its under surface is flattened or concave. Since the air passing over the top travels farther than the air passing under the wing, the air molecules are farther apart, thus less dense, on top of the wing than underneath. This difference in air density results in greater air pressure under the wing, which lifts the wing. Birds' bones are hollow and relatively light, allowing them to reach great speeds of flight. Some birds can fly up to 170 km, about 100 miles, per hour. Credit: National Geographic
