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Study reveals snapping power of a hummingbird's beak

posted 21 Jul 2011, 06:45 by Sam Mbale   [ updated 21 Jul 2011, 06:51 ]
The hummingbird's long, narrow beak is designed not just for sipping nectar from flowers but also for catching insects with remarkable speed and efficiency, according to a new study. Scientists from the National Evolutionary Synthesis Center in North Carolina say the birds can snatch flying insects in a fraction of a second thanks to a "controlled elastic snap" mechanism in their jaws.

  Hummingbirds cannot live on nectar alone. Scientists say they need the equivalent of 300 fruit flies each day to survive but armed only with a long narrow beak, how do they manage to catch their prey?

Gergor Yanega, Postdoctoral Fellow of the National Evolutionary Synthesis Center in Durham, North Carolina, wanted to find out.

Earlier research undertaken with University of Connecticut biologist Margaret Rubega had established that part of the answer lies in the bill's flexibility.

Using high speed video of three hummingbird species catching fruit flies, the researchers found that the hummingbird's bendy lower beak flexes by as much as 25 degrees when it opens, while also widening at the base to create a larger surface for catching insects.

But more recent research has revealed something else. While reviewing the ultrafast videos, Yanega noticed that as soon as the hummingbird's beak is maximally bent, it suddenly springs back to its original position and snaps closed. This "controlled elastic snap" allows the bird to snatch up flying insects in less than a hundredth of a second with greater speed and power than could be achieved by jaw muscles alone, says Yanega.

Yanega teamed up with engineers Matthew Smith and Andy Ruina of Cornell University to unlock the secret to the hummingbird beak's sudden snap. Armed with data on the length, thickness, and density of the bones and muscles in the hummingbird's head, the researchers developed a mathematical model of the elastic energy in the beak from the time it flexes open to the time it snaps shut.

Part of the trick lies in how the hummingbird's beak is built, the authors said. While other insect-eating birds such as swifts and nighthawks have a cartilaginous hinge near the base of their beaks, hummingbird beaks are solid bone.

"They're also incredibly thin," Yanega said. "This makes their lower beaks stiff yet springy, like a diving board."

The researchers' mathematical model revealed that the downward bend of the hummingbird's lower beak puts stress on the bone, storing elastic energy which eventually powers its sudden snap closure, explained first author Matthew Smith, now at the Air Force Research Laboratory at Wright-Patterson Air Force Base.

"The extra speed likely leads to greater success in catching insects," Smith said.

Known as snap-buckling, the phenomenon is similar to the opening and closing of a snap hair clip, Smith said. "Or, remember those little pop-up toys that consist of a half sphere made of rubber? When you invert one and set it on a hard surface it will eventually snap back into place and jump off the surface," Smith added.

Snap-buckling has also been observed in plants and insects. "The classic example of snap-buckling in plants is the venus flytrap, which uses this trick to catch insects," Smith said. "Cicadas, too, have tiny ribs which they snap-buckle to produce their distinctive song."

This study marks the first time snap-buckling has been observed in vertebrates, the authors added.

It will be published in a forthcoming issue of Journal of Theoretical Biology.