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Friday, November 16, 2012

Why Do Flocks of Geese Fly in a “V” Shape?

by Matt Soniak - November 14, 2012

(...) One reason­first proposed by aerospace engineers Peter Lissaman and Carl Shollenberger in 1970­is that the shape of the formation makes the birds more energetically efficient flyers than they would be flying alone. As a goose flies, air rushes around its wings, creating circular, rotating patterns of air at the ends of the wings called wingtip vortices. The vortices push air downward and upward in different spots (you can see a pretty clear illustration of this here), and if another goose is flying in one of the spots where the air is getting pushed up, it gets some free lift (the air force that directly opposes the goose’s weight) from the efforts of the first goose.

If geese fly in a group and arrange themselves correctly, then every one behind the leader gets a little extra lift and doesn’t have to flap as much to maintain altitude and forward momentum. The less they flap, the more energy they conserve, and the farther they can fly. (...)

Researchers have noticed something funny with some bird flocks: While the birds usually fly in positions that give them some energy benefit, not every bird is always in the expected optimal position, and therefore they get lower energy savings. Some birds just aren’t making the most of the “V,” which got people thinking that there might be another reason for the formation.

That reason might be that the formation allows the birds to maintain visual contact with each other and to communicate, making it easier to keep the group together and navigate. Taking the angles of the formation and what they know about geese’s field of vision and “blind spots” into account, researchers from the University of Rhode Island hypothesize that a “V” angle of 29 degrees or more would allow every bird in the group to see every other bird. There don’t appear to be any studies that directly test this idea. (...)

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