March 30, 2005

Cornell Scientists Explain Vampire Bat Locomotion

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Move over, Batman. There’s a new Superbat in town.

The common vampire bat (Desmodus rotundus) already can hang from ceilings, zip around the air and walk on the ground with ease. Now, two Cornell researchers have discovered that this native Central and South American species can also run, but in a way no one has seen before.

These bats propel themselves forward using their powerful winged forelimbs, moving with a bounding gait not observed in any other animal.

“It kind of looks like running push-ups,” said Daniel Riskin grad, a veterinary student studying terrestrial locomotion and one of the researchers.

Riskin and other scientists have long known this species’s talent in walking and hopping. “If you put them on the floor, most bats flap their wings. Other bats struggle across the floor with great difficulty,” he said. “Vampire bats can two-step.”

To find out more about how these bats move on the ground, Riskin traveled with Prof. John Hermanson, biomedical sciences, and field assistant Gerald Carter ’05 this past summer to Trinidad, an English-speaking island in the Caribbean where vampire bats are considered a pest species.

Once on the island, the researchers caught vampire bats by laying nets around cows, whose blood these bats feed upon. They put the bats on a special treadmill in a plexiglass cage and filmed the animals’ movements on the machine as its speed gradually increased.

At low speeds of 0.12 to 0.56 meters per second (0.27 to 1.3 miles per hour), the vampire bats tucked their wings out of the way and walked on their wrists and feet in a way similar to dogs.

What surprised him, Riskin said, was that “when the treadmill got going really fast, they started running.”

At speeds of 0.28 meters per second to 1.14 meters per second (0.63 to 2.5 miles per hour), the vampire bats broke into their unique, forelimb-driven bounding gait.

Carter, who was filming the bats at the time, was completely taken aback.

He recalls asking the other two, ‘”What is that? What are they doing?”‘

“I was expecting that they would give me some kind of answer, but they just looked at each other and everyone had their eyes wide open,” he said. “That’s when I realized that if they had never seen it, no one had seen it.”

His thought at that moment was, “Wow, we’re the first people in the world to see a bat running in that way.”

“It’s like a front wheel drive, that’s what Dan calls it,” Carter said about the bats’ motion. Riskin and Hermanson explained in the science magazine Nature, where their study was published, that the bats have this unique gait because ” … the forelimbs instead of the hindlimbs are recruited for force production as the wings are much more powerful than the legs.”

“On a bigger treadmill, [they] could go at least twice as fast as we had them going,” Riskin said.

Unlike cats and dogs that inherited their ability to run from a common ancestor, “vampire bats evolved the ability to run by themselves,” Riskin said. He believes they may have done so in the days when they were feeding on animals smaller and nimbler than cows, pigs and horses. If their prey moved away as they were feeding, vampire bats could just run a short distance after them instead of flying to catch up with them.

These bats’ terrestrial agility comes in handy when they maneuver around prey many times larger than they are. Cows, for example, can step on them and crush them if they do not get out of the way.

“Vampire bats are good on the ground because it’s very dangerous … they need to be quick,” Riskin said.

Footage of the bats running was an eye-opener for many biologists.

“I was totally surprised,” said Thomas Kunz, a bat expert and director for the Center for Ecology and Conservation Biology at Boston University. “I’m well aware that bats can run … the uniqueness of the discovery is the galloping locomotion they use.” He continued, “It raises questions about what kind of terrestrial locomotion might be present in other bats.”

To help answer that question, Riskin next plans to study the ground movement of an insect-eating New Zealand bat and compare its walk to that of the common vampire bat.

Understanding how these animals move is important, Hermanson said, because “a lot of the information about biology can be translated into other fields.” He pointed out that the Mars Rover, for example, draws upon the locomotion patterns of several animals in its design.

Archived article by Xiaowei Cathy Tang
Sun Senior Writer