Flight in V Formations
The geese have been flying over for several weeks now. Those “V formations” are the topic of a common joke. I assume you have heard the one about why there always seems to be more geese in one arm of the V than the other? It is because there are more geese in that side. But on a more serious note, why is it that waterfowl fly in a V formation?
As reported in Science online, a recent study published in the scientific journal Nature used bald ibises, a long legged wading bird, to better understand the aerodynamics of birds flying in a V formation. They attached data loggers with GPS units to 14 of the birds. This enabled the scientists to determine all the birds’ locations to within 30 centimeters or about a foot. What the scientists discovered was, and I quote the Science report here: “the birds positioned themselves to fly just behind and to the side of the bird in front, timing their wingbeats to catch the uplifting eddies.” So the birds are apparently finding a position and timing their wingbeats to obtain greater lift from the bird in front of them in formation compared to if they simply flew alone. This would be a type of drafting, and presumably the birds conserve energy although this particular study did not collect data on energetics.
Most any cyclist or fan of the Tour de France has learned that drafting saves energy. A cyclist creates a wake of vortices, some of which can cause a low pressure area behind them. So if another biker can get into this “sweet spot” or “slipstream” just behind and to the side of the rider in front of them, they may save a considerable amount of energy. Some estimate the energy savings may be as high as 40%. The person drafting certainly benefits, but the vortices may also benefit the lead biker as well. Like birds flying in a V formation, bikers will periodically change positions so each biker benefits. And of course the energy savings would be considerable over long distance travel.
It has been estimated that the energy savings for birds flying in a V formation may be anywhere from 20-30%. It is interesting to note that the birds that fly in a V formation are fairly large social birds such as ducks, geese, swans, cranes, and pelicans. It is thought that the aerodynamics of flocks of small birds is so complex, that flying in a V formation just wouldn’t work.
So the next time you see a flock of geese or some other birds flying in a V formation give some consideration to the aerodynamics produced by the flock. Then give some thought of how these birds are able to use those vortices and presumably save energy on their long distance migrations.
Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.
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