It’s a classic sight during migration: geese flying overhead in a perfect V-formation. At first glance, the behavior is simple. Scientists and some lay-birders know the V-formation helps conserve energy over long flights. As birds fly, air flows over and around their wings. This change in air flow makes it easier for birds behind to fly.
If you’ve ever been on a bike ride with a friend, you may have noticed a similar dynamic. Biking immediately behind another cyclist cuts wind resistance and can save nearly 30 percent of a biker’s energy. This technique—drafting—explains the theory behind the big pelotons you see in cycling races. Likewise, military airplanes often fly in V formations to save fuel.
For birds, flying in a V works in a similar manner. In practice, however, it is far more complex.
The Science Behind the V Formation
As a bird flies, the air passing over its wings is disrupted.
When air moves over top of a wing (bird or plane), it is flows faster than the air below it. The air that has traveled over the wings pushes down onto the still air below. In turn, the air behind the bird’s body pushes up, creating a swirling vortex of air flowing behind and to the side of the bird. The air moving up helps create “lift” for the next bird in the V formation. Able to use this updraft of air for lift, the bird flying behind uses less energy than if it were in front.
This extra energy isn’t just a nice perk. For birds with long migratory ranges, it’s a necessity. One scientific study theorized that 25 birds flying in a v-formation can increase their range by about 70 percent. Geese migrate over thousands of miles, sometimes flying hundreds of miles without stopping. Snow geese can fly up to 600 miles in a single day.
How do Birds Know to Fly in a V?
While scientists have long understood that the v-formation results in easier flight for birds, they understood little about how and why birds fly in this manner. A 2014 study of northern bald ibises has helped shed even more light on this behavior.
Scientists fitted birds with data loggers as they migrated between Austria and Italy. They flew behind an ultralight aircraft which they had been taught to follow. As predicted, the birds positioned themselves in the ideal place to obtain the most benefit from the bird in front of them.
But for birds, the wake created from flying isn’t as straightforward as it is for a plane. Birds flap their wings—meaning the vortex created from their flight is always changing. But the researchers tracking the ibises found that the birds were able to adjust their own flapping in order to account for the wake created by the bird in front of them.
See also: How to Accurately Count Flocks of Birds
So not only do birds have to figure out the perfect distance to fly behind each other, they also have to know how to time their wing flaps in order to maximize the benefit of flying in a V. But the work is worth the effort. One study of pelicans found that the birds flying in formation had lower heart rates than those flying solo.
While the sight of the flying V is a common one for birders, the study of the ibises was one of the first glimpses into how the V formation actually works with free-flying birds. Before, most research on V formations had been mostly theoretical.
Questions Left Unanswered
And researchers still have questions. Do birds simply adjust their flight behavior based on what feels easier—or is flying in a V shape learned? Who gets (or rather, has) to be the leader? Why, and when, do they switch positions or move out of the formation? And are their other benefits to flying in a V besides expending less energy—perhaps better in-flight communication?
So as migratory birds start returning to their nesting grounds this spring, keep an eye out for V formations up above. There is still more to learn about how birds coordinate their flight.