Why Do Birds Fly in a V Formation? Breaking Down a Brilliant Migration Hack

The scene is a familiar one: A V-shaped flock of Canada Geese flies overhead, wings flapping languidly among the wisps of clouds as their discordant honks carry across the spring or fall air. The shape of the V might not always be perfect, but the birds remain true to the general form as it shifts, stretches, and contracts across the sky.

Conventional wisdom holds that flying in a V formation is a means for birds to conserve energy, and research has shown this to be true. But the aerodynamics and flock mechanics involved in this specific formation are more interesting and complex than the simple shape might suggest. In fact, scientists are still uncovering new details about how flocks of birds use basic V principles to hack aerodynamics and increase their efficiency. Read on to learn how exactly the V formation works and what type of birds benefit most from it.
 

How the V Works 

While flying, a bird creates the same aerodynamic forces as an airplane: In the space directly behind the bird, the air is pushed downward (downwash), and in the areas behind and to the side of its wings, the air is brought upward (upwash). This change in airflow direction is created by a vortex generated by the bird’s wing tips.

Bret Tobalske, a biologist studying flight mechanisms in birds at the University of Montana, compares this vortex phenomenon to the shape of a common childhood toy: a stretched out slinky. As the air turns in a swirling pattern behind a bird’s wing, the bird following can take advantage of the upward moving air to gain lift. “It’s like a surfer on a surfboard experiences upwash from a wave,” Tobalske says. “It's energy in the environment that's helping to assist this bird behind it, because this air is moving upwards.” 

When birds fly in a true V formation—with one bird in the lead and each successive bird staggered behind and slightly to the left or right of the preceding bird—the upwash created by the bird in front provides lift to the bird directly behind, reducing how much it needs to flap. Some studies suggest the V could provide up to 10-14 percent of energy savings for the trailing birds.  

While Canada Geese are perhaps the most famous species to fly in a V, cranes, cormorants, ducks, swans, and pelicans are also known to use this strategy. In a 2001 study attaching heart monitors to a group of Great White Pelicans, data showed that, due to the reduction in flapping, the heart rates of the birds in the back were less than the leading bird, resulting in up to 11 percent energy savings overall. 

There’s a good reason why birds that use the V trend on the larger side: Size creates an advantage for this flight formation. Tobalske points to the slower flapping speed required with a bigger body instead of, say, the quicker, more erratic flaps of smaller birds. Though we can’t see it with our eyes, the upwash created by bigger birds allows for the optimal aerodynamics in V-shaped flight. “In smaller formations with smaller birds, their wake structure might not persist, it might decay,” Tobalske says.

Who Leads the V?  

All or most of the birds in a flock will eventually take the lead spot. You might have seen geese in flight change leaders, and that usually happens when the lead goose grows tired from forging the way for the others through “clean air.” In this case, a trailing bird will assume the new leader role until it grows weary. And so on. 

In one study, researchers found that flocks of Northern Bald Ibis took turns frequently, and oftentimes, a pair would split off from the main group, sharing roles evenly to ensure both birds benefited from the upwash. The ibis in the study relied on visual cues like wing-flap timing to best position themselves behind the bird in front, as well as knowing when to change places to avoid over-exhaustion in the lead bird. 

Interestingly, despite how integral this behavior is for certain species, young birds have to learn how these group dynamics and the physics of the V work. Research conducted with young Northern Bald Ibises in 2014 found that they lacked an innate understanding of the V but were quick to fall into formation once they developed a sense for the energy-saving benefits and how the system works.

Behold, the Compound V

More recently, to better understand how aerodynamics works within a more typical flock of birds in flight, researchers at the University of North Carolina at Chapel Hill conducted a 2019 study analyzing flocks of shorebirds, including the American Avocet, Dunlin, Short-billed Dowitcher, and Marbled Godwit. The work was led by postdoctoral researcher Aaron Corcoran and UNC professor Ty Hedrick.

Analyzing footage of the various flocks, the duo used 3D technology to create visual lines depicting each bird’s path and the flock’s overall structure. As they recorded the precise distance the birds aligned themselves in, the team was able to identify a pattern that they dubbed the “compound V-shape.” Each bird, regardless of species or size (some of the flocks were mixed), maintained one wingspan to the side and one and a half of a wingspan behind the bird in front of them while in a large flock. The findings suggest that birds in flocks still use basic principles of V aerodynamics but on a much smaller and tighter scale. 

“It's one of those things that, once you know the pattern is there, then you can't unsee it. Your eyes are just drawn to these lines,” Corcoran says. “The whole thing makes this sort of beautiful symmetry and geometry.”