It’s an iconic image of fall—a V of geese high overhead, migrating south for the winter. Several other bird species, such as flamingos, also fly in V formations, but geese are the most well known. On any given fall day, numerous Vs can be seen passing gracefully below the clouds. Most birds actually don’t migrate in the V formation; smaller birds tend to fly in huge amorphous flocks. Others fly in a simple line. But why do geese and other birds fly in V formations?
Writing in the journal “Auk,” John Badgerow examined numerous formations of geese, hoping to come up with a definitive answer. Aerodynamism was not initially seen as a primary reason for the behavior; previous analyses had suggested that the birds were too far apart to benefit from the energy saved. Instead, the angle of the V suggested that the primary purpose was a form of visual communication—the geese that composed both diagonal lines, each slightly angled from one another, would have an unobstructed view of the lead goose who determined the flight path of the flock.
Badgerow, unconvinced, decided to test both hypotheses. Working from film, he analyzed the geometry of the formations. Badgerow calculated that maximum energetic advantage (compared to solo flight) is achieved at exactly 0.16 meters between the wingtips of a bird and the one following. The spacing requirements explain why only certain birds fly in V-formations—only birds with large wingspans and slow beats can achieve the energy saving. Rapid or erratic flapping creates too much wake turbulence, which disrupts the formation. Migrating geese effectively function like airplanes.
At the same time, information about changes in course and velocity must be communicated to other members of the flock, so visual communication does play a role. The angle seems to be chosen so all members of a flock can see the leader and adjust to any changes. Flocks contain both experienced and new migrants, so communicating information about rest and feeding areas is vital.
In practice, turbulence, air currents, and other factors make it extremely difficult for the geese to maintain the exact spacing needed to maximize efficiency or communication, and actual efficiency improvements are only about 20% of the theoretical maximum. Geese go to great lengths to maintain their formation as best as possible, so Badgerow suggests that while both communication and efficiency play a role in V-formations, energy efficiency is the primary motivator. More recent studies have confirmed that flying in the lead is the most tiring position, so geese take turns at the head of the V in order to allow leaders to rest.