Saturday, January 19, 2008

Formation flying has hidden advantages

The sight of a flock of geese flying overhead in the familiar V-shape formation often please observers on the ground, but there is more to this formation flying than just its beauty. Some birds, such as geese and cranes, migrate over vast distances. Rare Siberian cranes, for example, fly from their wintering grounds in India and China to their breeding grounds in Siberia and back again each year. By flying in a V-shape the birds save energy, as each receives a boost from the bird in front. Flapping wings produce small eddies of air at their tips. These swirls of turbulence are a nuisance to the bird producing them as they act as a drag on flight. But they help a bird following a little way behind, because the upwash of air provides extra lift, so the bird does not have to work so hard to stay airborne. The best effect is achieved if the birds fly with wing tips overlapping, but there is still some benefit in loose V-formations.

Snow geese will often fly slightly behind and above the bird in front, with the head adjacent to the neighbour's wing tip. This configuration gives each bird a better view of where it is going. By flying in a V-formation, the birds in front help the ones behind to save energy and therefore the group can fly farther for the same amount of 'fuel'. The leading bird receives no help, so every now and then it drops back and another takes the lead.

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