Vampires Run: Bats on treadmills show high-speed gait

Susan Milius

Vampire bats have evolved their own form of running, the first test of these creatures on a treadmill shows. As the treadmill pace picks up, they switch to a run, with all limbs airborne at one point in each stride.

These are the only bats known to run, so their ancestors probably didn't go jogging, reports Daniel Riskin of Cornell University.

"Because vampire bats evolved the ability to run independently of other runners, they're a separate group for people to test their hypotheses on," Riskin says. The news comes as a surprise, comments John Hutchinson of the Royal Veterinary College in London. "It's one of the few—or only—examples I can think of in which a lineage has re-evolved running."

Riskin started out studying how bats of various species move across a surface, which they generally do badly. The least effective of them "just smack their wings against the ground and freak out," never successfully taking a step, he says.

Other species can shuffle. "The typical bat can get from A to B, but it looks really clumsy while it does it," Riskin says.

In contrast, he ranks the ground-traversing skills of vampire bats as "off-the-scale good." The 8-centimeter-long animals move nimbly in any direction, easily making the transition from ground to air movement. They can jump into flight from a standing start in some 30 milliseconds.

That's a useful skill for an animal that can spend 40 or so minutes at a time licking a small cut that it makes on a bigger animal. All three species of vampire bats require blood meals to survive. The common vampire bat (Desmodus rotundus), which Riskin studies, prefers cattle as a blood source. Riskin tested wild bats in Trinidad by setting up fine netting at night around a cluster of cattle and capturing bats that flew in for dinner.

He placed each bat inside a cage about the size of an elongated shoe box with a customized treadmill as the floor. At first, the bats strolled along. When Riskin sped up the treadmill to more than 0.5 meter per second, he was startled to find that bats started bounding, pushing off with their powerful forearms. The maximum speed clocked was 1.2 m/s.

"It's not often in science that you have the eureka moment like we did," says Riskin. "I'll always remember just looking over at my coauthor John Hermanson and he looked back at me, and we just started laughing." They report their finding in the March 17 Nature.

Rodger Kram of the University of Colorado in Boulder is intrigued by the work. He notes that the bats use both wings in sync for running as well as flying. He comments that besides the bats' reinvention of running, "the biggest point is that the muscle-tendon systems are so versatile. Few human-made machines can act like springs, motors, and brakes."

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References:

Riskin, D.K., and J.W. Hermanson. 2005. Biomechanics: Independent evolution of running in vampire bats. Nature 434(March 17):292. Abstract available at http://dx.doi.org/10.1038/434292a.

Further Readings:

Hutchinson, J.R. … and R. Kram. 2003. Biomechanics: Are fast-moving elephants really running? Nature 422(April 3):493–494. Abstract available at http://dx.doi.org/10.1038/422493a.

To see a short QuickTime movie of a vampire bat running, go to http://www.sciencenews.org/articles/20050319/RISKIN.MOV.

Sources:

John Hermanson
Department of Biomedical Sciences
College of Veterinary Medicine
Cornell University
Ithaca, NY 14853

John Hutchinson
Structure and Motion Laboratory
Royal Veterinary College
University of London
North Mymms, Hatfield
Herts AL9 7TA
United Kingdom

Rodger Kram
Department of Kinesiology and Applied Physiology
University of Colorado, Boulder
354 UCB
Boulder, CO 80309-0354

Daniel K. Riskin
Department of Biomedical Sciences
College of Veterinary Medicine
Cornell University
Ithaca, NY 14853

From Science News, Volume 167, No. 12, March 19, 2005, p. 179.