Why Not a "P" or "Q"?

by Charlotte Overby
illustrated by Dave Besenger

When it comes to flying in groups, geese choose the right letter.

Air spilling from the end of a goose's flapping wind creates a spiraling eddy of rising air. A goose flying behind and to the side of another will have a wind in this air current. The upward push the current provides makes it less tiring for the goose to stay aloft.

People love to ask difficult questions. For example, why do geese fly in a "V?" Since geese can't tell us, biologists must look at evidence, make careful observations and call upon their experience to come up with reasonable, likely explanations. Ornithologists-people who study birds-may never be 100 percent sure they know why geese fly in a "V" formation. But they can examine wind resistance and aerodynamics to offer a sound explanation.

If you have ever watched a bicycle race, you know that cyclists stay hunched over their handlebars, keep their elbows tucked in and wear sleek, aerodynamic helmets. To win, they do everything they can to overcome resistance from the wind.

One of the best ways for cyclists to overcome wind resistance and go faster is to ride behind each other in a long column. That way, when you are right behind an opponent, he's doing the extra work of cutting through the air. You can save your energy and pull ahead with a final burst of speed near the end of the race. Cyclists use straight line formation to race efficiently, and what works for cyclists works for other creatures, too.

Like cyclists, geese fly in formation, probably to save energy. But the formation they use is shaped like the letter "V." Why do they fly in a "V" formation rather than a straight column?

In many ways, a goose's job is tougher than a cyclist's. Not only do geese battle wind resistance, they must also stay aloft. They have to both buck the wind and fly.

To accomplish this, geese are equipped with curved wings that taper-or grow narrow-at the tip. The top surface of their wings bulge upward, while the bottoms are flatter. Air moves more quickly over the bulging top of the wing, creating an upward suction. This upward pull is called "lift," and it is what keeps birds in the air.

But lift is an interesting phenomenon. While a goose is tugged upward, some air spills away from the tips of its wings too, creating an updraft. This updraft spreads out behind the goose in a V-shape, similar to the wake left in water behind a boat.

If another goose flies with a wing inside this updraft "wake," it gets an added boost and feels less wind resistance. Ornithologists have observed geese taking turns leading the "V," and even young birds lead at times. This suggests that when a goose gets tired of fighting the wind, it moves back to a new position in the "V" to save energy.

Charlotte Overby is assistant editor of the Conservationist magazine.