Buzz
During this time of year, it’s nearly impossible to travel through large parts of the U.S. without seeing a Canada Goose. These birds migrate south from Canada for the winter, and in some regions, they stay all year. When not resting in fields or by streams, they’re often seen flying overhead, typically in a ‘V’ shape, with one goose leading the way and the others forming two diverging lines behind it.
What’s the purpose of the ‘V’ formation? It’s not just because a ‘Q’ would be too complex. Scientists have discovered that this arrangement has two key benefits that make it easier for the group to travel together.
Give Me A Lift
One reason, initially suggested by aerospace engineers Peter Lissaman and Carl Shollenberger in 1970, is that the ‘V’ formation makes the birds more energy-efficient flyers compared to flying solo. As a goose flaps its wings, air flows around them, creating rotating air patterns at the wingtips known as wingtip vortices. These vortices push air both upward and downward in varying spots (a clear illustration of this can be found here), and when another goose flies in a spot where the air is being pushed upward, it receives free lift—air that opposes its weight—from the efforts of the first goose.
When geese fly in a group and align themselves properly, each bird behind the leader benefits from extra lift, requiring less effort to maintain altitude and speed. With less flapping, the birds conserve more energy, enabling them to fly further.
For years, scientists only had mathematical models, photos, and distant observations of geese in flight to support this hypothesis. The aerodynamics seemed logical, and birds were often observed in positions that suggested they were benefiting from the formation, but no one had directly measured the energetic advantages, if any, for birds flying freely.
Then, in 2001, French scientists were presented with a rare opportunity to measure these benefits firsthand when they collaborated with a film company that had trained great white pelicans to fly in formation behind motorboats and ultralight planes for movie scenes. The team from the Centre d'Etudes Biologiques de Chizé, led by ecologist Henri Weimerskirch, outfitted the birds with heart rate monitors and filmed their flight. The data revealed that pelicans flying in ‘V’ formation had heart rates that were 11.4–14.5 percent lower than those of birds flying solo, and that the birds in formation flapped less and glided more, resulting in energy savings of 11.4–14.0 percent.
Given these findings, why don’t all birds fly in a ‘V’? It turns out the benefits of this formation are more pronounced for larger birds like geese and pelicans, and not as effective for smaller, lighter birds. However, other flight formations may have their own advantages. For instance, the ‘cluster’ formations that pigeons use, while actually costing them energy compared to flying alone, may allow large groups to fly closely together, making it easier to maneuver and turn without colliding mid-air.
An Eye on You
Researchers have observed an interesting phenomenon with some bird flocks: while the birds typically fly in positions that offer energy savings, not every bird is always in the most advantageous spot. As a result, some birds don't fully benefit from the ‘V’ formation, leading researchers to consider that there might be another reason for the birds' flight arrangement.
This reason could be that the formation helps the birds maintain visual contact with one another and communicate, making it easier to stay together and navigate. By factoring in the angles of the formation and the birds' field of vision and ‘blind spots,’ researchers from the University of Rhode Island suggest that a ‘V’ angle of 29 degrees or more would allow all the birds to see each other. However, there don't appear to be any studies that directly test this hypothesis.
Much like the energy conservation idea, though, the birds don’t always choose the optimal spot for clear visual contact. Most often, they fly in positions that provide some benefit in terms of energy, group cohesion, or both. These near-optimal situations raise the question of whether there’s another advantage to the ‘V’ that we haven’t yet identified, or if it's simply challenging for birds to find and maintain the best position in the formation.
