As with an airplane, four main forces affect the flight of a bird: lift, drag, thrust, and the downward pull of gravity. To overcome gravity, birds must generate lift, the force that takes them upward. Air flowing over and under their specially-formed wing creates lift, but the airflow also pushes the wing back with a force called drag. When lift and drag are combined, an upward and backward force results. To overcome this, birds creates thrust by flapping their wings to move themselves forward.

A bird wing is very stream-lined, tapering from a thick, rounded leading edge to a thin point at the trailing edge. Because the wing is concavely curved, air traveling over the upper surface has to cover a greater distance and moves faster to catch up with air taking the shorter bottom route from the front to the back of the wing. This fast-moving air creates a low pressure zone along the upper surface of the wing. With low pressure above and higher pressure below, the wing is "sucked" up.

Birds with different types of flight have wings that are shaped very differently.

Many seabirds, like albatrosses, have long, narrow pointed wings for gliding long distances over the ocean into the ocean winds. The length generates lots of lift, while the narrow, pointed shape helps reduce drag while gliding.

Long, broad eagle wings have a large surface area for soaring on rising warm air currents. The spaces between the feathers at the end of the wing help reduce drag and are used for fine control at slow speeds. Storks, pelicans, and hawks have wings similar in shape.

Short rounded wings allow pheasants rapid takeoffs, good maneuverability, and short glides. Many forest birds have small rounded wings that are good for quick, sharp turns while flying among trees.

Similar to a high speed jet, swallows have relatively small, narrow, tapering wings. These wings can be flapped rapidly to provide speed with little drag. The fastest flyers in the bird world, falcons and swifts, have wings of this shape.

Birds fly by flapping or gliding. Flapping takes tremendous energy, so many birds, such as jays and woodpeckers, follow bursts of flapping flight with gliding flight. Some larger birds have developed wings that let them soar and glide for long periods without flapping. Hummingbirds, with their tiny wings, can hardly glide at all.

On the upstroke of the wing beat, the feathers at the end of many bird wings twist sideways to let the air slip through with little resistance. The down stroke is the power stroke. Rather than rowing a bird through the air, the wings act like the propeller on an airplane to pull the bird forward.

Darting from flower to flower, hummingbirds fly like tiny helicopters. They can hover or quickly move forward, backward, sideways, straight up or straight down. Some hummingbirds flap their wings as many as 100 times per second to accomplish these maneuvers. Their unique shoulder joints also turn the wings upside down on the backstroke, enabling the wing's path follows a figure-8 pattern.

Classroom Activities: Paper "Bird" Contest Bird's Eye Story