With greater speed and power than could be achieved by jaw muscles alone, the shape of a hummingbird's beak allows for a “controlled elastic snap” that allows it to snatch up flying insects in a mere fraction of a second, says a new study in a forthcoming issue of Journal of Theoretical Biology.
Not nectar alone
Hummingbird beaks are built to feed on flowers, but hummingbirds can't live on nectar alone. To get enough protein and nutrients they need to eat small insects too, said co-author Gregor Yanega of the National Evolutionary Synthesis Center in Durham, North Carolina.
But how can a long, slender bill so well suited for sipping nectar also be good at catching insects, and often in mid-air?
In 2004 in the journal Nature , Yanega reported that part of the answer lies in the hummingbird's flexible bill. 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 , according to a National Evolutionary Synthesis Center press release.
While watching the ultrafast videos, however, Yanega also noticed something else: As soon as the hummingbird's beak is maximally bent, it suddenly springs back to its original position and snaps closed.
“Their beaks snap shut in less than a hundredth of a second,” he explained. “It's fast.”
Yanega teamed up with engineers Matthew Smith and Andy Ruina of Cornell University to unlock the secret to the hummingbird beak's sudden snap.
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.
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.
