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Bat flight secrets revealed

Scientists have discovered how bats' wing motions help them stay in the air. The research shows that bats and birds use their wings quite differently.

These findings should interest biologists, because they reveal a new way that nature has solved the problem of how to fly. They may also be useful for engineers who want to design new types of flying machines.

An important difference between bird and bat flight is that bats have a thin membrane that stretches across each wing. The membrane pushes the air out of the way when the wing moves both up and down.

Birds, on the other hand, can separate their wing feathers, sort of like the slats on a Venetian blind. They close the feathers so that the wing pushes against the air on the downstroke. But, they open their feathers on the upstroke, so air can move through the wing.

These two types of wings create very different "wakes" in the air as they move. A wake is the movement of air (or other substances, like water) that happens after an object moves through.

Researchers have learned a lot about bird flight by studying the wakes that the birds create while flying in a wind tunnel. Anders Hedenström of Lund University in Sweden and colleagues conducted similar experiments with a species of small, nectar-feeding bat.

They used a fog machine – the same kind that's used during performances on stage – to fill the wind tunnel with fog. Then they used a special camera to help them see the movement of the fog particles in the bats' wake as the animals flew in the tunnel.

By looking at the way the bats' wing motions affected the air around them, the researchers began to understand how bats stay in the air. For example, when the bat is moving slowly, it gives its wings a little backwards flick during the upstroke, and this helps lift the bat into the air. These flight trucks turned out to be quite different from the ones used by birds, the authors say.

This study appears in the 11 May issue of the journal Science.