Why Do Geese Fly in a V Formation? Saving Energy in Flight

How the V formation saves energy

As a bird flaps, air flows around the tips of its wings and forms spinning wingtip vortices. Directly behind the bird, this air moves downward, called downwash, which would push a following bird down. Just outside the wingtip, however, the air spirals upward, called upwash.

A goose positioned in that upwash gets a little free lift, much as a glider gains height in rising air. It needs to flap less hard to stay aloft, so it uses less energy. Because every bird except the leader can sit in the upwash of the bird in front, a diagonal line, or two lines making a V, is the natural shape.

The idea was first suggested by the German engineer Carl Wieselsberger in 1914, based on what was known about aircraft wings. Airplanes flying in formation can save fuel for the same reason, and aircraft makers have tested the idea.

What the research shows

For decades the energy-saving theory was based on calculations. Since around 2000, experiments with real birds have tested it.

In the pelican study, trained birds flew behind a boat or a light aircraft, and those in formation flapped less often and had lower heart rates than those flying alone, a clear sign of energy saving.

The ibis studies were possible because conservationists were teaching young northern bald ibises a migration route by leading them with a microlight aircraft. Each bird carried a tiny data logger that recorded its position and every wingbeat. The birds placed themselves close to the best aerodynamic positions and timed their flapping to match the bird in front, so their wingtips followed the path of the rising air. When a bird ended up directly behind another, it flapped out of step, which reduces the effect of the downwash.

No one has fitted wild Canada geese with the same equipment, but geese are large, long-winged birds that migrate long distances, exactly the kind of flier expected to benefit most.

Who leads the V?

Flying at the front is hard work, because the leader gets no upwash from anyone. For this reason geese and other formation fliers take turns in the lead.

The 2015 ibis study found something remarkable: birds tended to pair up and swap positions, so each individual spent roughly as much time leading as it did following and benefiting. Scientists see this as a form of cooperation by direct reciprocity, a kind of “I help you, you help me”. Leaders drop back into the line to rest, and another bird moves forward.

In Canada geese, flocks are usually made up of families and related groups, and young birds learn migration routes by flying with their parents. The lead position is not reserved for a single “boss” goose.

The V helps geese see and communicate

Saving energy is probably not the only benefit. In 1967 the zoologist W. J. Hamilton suggested that a staggered V gives every bird a clear view forward and of its neighbors. This makes it easier to keep a safe distance, avoid collisions and follow sudden changes of direction.

Many scientists think both explanations play a role: the V is the shape that lets large birds fly close enough to share upwash while still seeing one another. Geese also honk almost constantly in flight, which probably helps flock members stay in contact, especially at night or in cloud.

Why the V is not always perfect

Real goose formations are rarely neat textbook Vs. Flocks often fly in a single diagonal line called an echelon, a J shape, a wavy line or a loose cluster that keeps changing. Birds join and leave the formation, wind gusts push them out of position, and one arm of the V is often longer than the other.

Formations are most common during long, steady flights such as migration. When geese fly short distances between a roost and feeding fields, they often travel in looser groups.

Which other birds fly in a V?

V and echelon formations are typical of large birds with long wings that travel long distances, including:

• Geese and swans
• Ducks, such as the mallard
• Cranes and ibises
• Pelicans and cormorants
• Some gulls

Small songbirds rarely fly in tight formations; many of them migrate alone or in loose flocks at night.

For more on the long journeys these formations make possible, see do Canada geese migrate? and why do birds migrate?.