(2 of 2)
Helicopters & Catapults. Some birds are helicopters. A hummingbird's wings are pivoted so that they can beat horizontally, always keeping their leading edges forward in the stroke. When the hummingbird hovers beside a flower, its fast-beating wings, just like the spinning blades of a helicopter's rotor, provide lift only. Wood ibis are helicopters only on the takeoff. When frightened, they whir up nearly vertically; then they settle into normal flight when they feel that they are out of danger.
Other birds are gliders. Turkey buzzards and pelicans, for example, have "power," but they use it only on the take-off or during emergencies. Most of the time they soar on motionless wings, riding on "up-currents" of air. Such birds (like men's gliders) have long, narrow wings, the most efficient shape for gliding. The wings of an albatross, probably the most efficient glider, have an "aspect ratio" of 11 to 1, i.e., its wings are eleven times as long as they are broad. A magpie, which, like a fighter plane, needs good maneuverability and seldom glides, has a low aspect ratio (about 2 to 1).
Some birds use a catapult take-off like the scouting planes carried on cruisers—e.g., egrets give themselves initial flying speed by a powerful push from their legs. Other birds need a long take-off run. Condors head into the wind like airplanes and run along the surface of the land, flapping their wings frantically until they at last reach flying speed. Andean Indians sometimes trap condors by tricking them into landing on bait encircled by low stone walls. Then the foolish condor is helpless, like a bomber that has made an emergency landing on a small field and cannot take off again.