Takeoff, Climbing, and Steering

When a bird takes off, it usually does so into the wind, like an airplane. To get airborne, it must produce enough for­ward momentum to generate lift. A small bird takes a short run or jumps into the air from a perch, such as a branch. A large, heavy bird needs a takeoff run, just like most airplanes. Water birds, such as ducks, often skitter across the surface of water, paddling with their feet to build up speed. Swifts have short legs and seldom walk on the

WING SPEEDS

Tiny hummingbirds flap their wings so fast-more than fifty times per second-that the wings are just a blur. The fastest wing beat of any bird is that of the horned sungem, a South American hummingbird species that beats its wings ninety times per second. A heron needs to flap its wings only two times per second, and condors can stay in the air for 50 miles (80 kilometers) or more, using air currents, without beating their wings once.

more than fifty times in a second.

ground. They just drop from their nests and open their wings.

To climb higher through the air, a bird tilts its wings to increase the angle of attack. This action pushes more air over the top of the wing. If the angle became too steep, turbulence in the airstream could cause the bird to stall—
it would stop climbing and could start falling. To prevent a stall, the bird uses a tuft of feathers (called the alula) on its “thumb.” This tuft can be spread forward to form a slot on the leading edge, or front of the wing. Air rushes through the slot, preventing turbulence and keeping a fast flow of air over the wing. In nor­mal flight, the tuft is folded back against the wing. This is similar to the slots and flaps used on the wings of airplanes.

A bird steers by tilting its body and wings and using its tail as a rudder. Birds can twist and turn sharply to avoid obstacles (such as tree branches) and to escape a pursuing predator. Tail shape does not seem to affect a bird’s control very much. A swift twists and turns when chasing flying insects, yet it has a short tail. Swallows fly very similarly, at high speeds, with long, forked tails. A partridge can turn sharply using its broad wings rather than its stubby tail.