Species evolved its galloping gait independently of other mammals.
Vampire bats' thirst for blood has driven them to evolve an unexpected sprinting ability. Most bats are awkward on the ground, but the common vampire bat can bound along at more than 1 metre per second.
Researchers made the discovery at a ranch in Trinidad, with five adult male vampire bats (Desmodus rotundus), which they caught using cows as bait. They put the bats on a treadmill inside a Plexiglas cage and recorded their movements with high-speed video.
"We knew they could hop and are very fast, but we weren't expecting this. Instead of walking fast, they ran," says Daniel Riskin of Cornell University in Ithaca, New York, who reports the results in this week's Nature1.
“We knew they could hop and are very fast, but we weren't expecting this. Instead of walking fast, they ran. Daniel Riskin , College of Veterinary Medicine, Cornell University”
The bats' gait fulfilled the definition of 'running' because their strides took them completely off the ground, as when a horse runs. But their style was quite different from anything the researchers had seen in other mammals (see video).
As the bats are built for flight, with winged forelimbs that are much stronger than their hind legs, they have developed their own unique running technique. They land on their hind legs, rock forwards on to their wrists, then launch themselves up and forward with their forelimbs before landing again on their back legs.
Research suggests that bats (Chiroptera) lost effective terrestrial locomotion early in their evolutionary history, so it seems the vampires must have evolved it anew. "The vampire bat doesn't look like any other animal that runs," confirms Riskin.
In the wild, vampire bats feed on the blood of large animals such as cattle, horses and pigs. They sneak up over the ground and make small incisions in the skin (usually the heel) of sleeping prey.
"Bats take a long time to feed," explains Colin Catto of the London-based Bat Conservation Trust. "If they were trying to hover for all that time they would expend an awful lot of energy."
The bats are most likely to run when moving between animals, and may have acquired the skill before the arrival of domestic livestock, at which point dinner became an easier meal.
Riskin believes that the top speed of these nimble creatures could be even more impressive than demonstrated. "If they weren't in the tight confines of a cage, the bats would run faster as they would be able to jump higher," he says.
Coupled with being agile and deft, Riskin's bats were also quick learners. After one short walk on the treadmill the bats mastered both the dynamics of the machine and recognized the purr of the motor. "Vampire bats are ridiculously smart," Riskin says. "As smart as a dog."
RiskinD. K. & HermansonJ. W. Nature, 434. 292 (2005).
College of Veterinary Medicine, Cornell University