Except for the occasional superhero, being able to fly through the air and run across the ground is a rare combination of skills. But a new study shows that vampire bats have mastered both modes of transportation.
Bats are the only mammals that can fly, but they've had to pay a price. The very features that enable them to soar--leathery wings and tiny legs--make it impossible for most bats to manage more than an awkward crawl on land. However, there have been reports that vampire bats sometimes scurry.
Intrigued by the rumors, John Hermanson, a biologist at Cornell University in Ithaca, New York, and his graduate student Dan Riskin, tested bats on a slowly accelerating treadmill. Not only can vampire bats walk at speeds comparable to similarly sized mice, they seem to have developed a unique method of running, the team reports in the 17 March issue of Nature. At lower speeds, the bats walk on all fours in a one-foot-after-the-other manner. But at about 1.8 kilometers per hour, they break into a true run, leaving the ground completely between strides. Since most of the vampire bats' strength is in their wings, the creatures have a gait unique among animals: thrusting with the front limbs and landing on the back--the opposite of that seen in most terrestrial animals.
No other bats tested by the team can run. And because there's nothing unique about vampire bat anatomy that would make them runners, Riskin and Hermanson argue that the capacity to run was a behavioral adaptation re-invented by vampire bats during their evolution. It may have proven especially useful because, unlike other bats, vampires sneak up on their prey from the ground. Being able to sprint in for a quick bite may have presented an advantage, and the genes encoding the behavior would have spread quickly in the species.
"What I find most intriguing about this study," says John Bertram, a biologist at the University of Calgary in Alberta, Canada, is the "mechanically sophisticated solution" the bats have discovered for running with wings. Bertram wonders if such behavior-driven innovations aren't "far more prevalent than we have appreciated."