Daniel Riskin is a self-confessed bat nut. He's mesmerised by these remarkable mammals. But it's not just their ability to fly that intrigues Riskin, `there's so much more to these animals' he says. Out of the more than 1 100 known species, only a handful have opted for a terrestrial life style,one being the common vampire bat. Riskin explains that these 30 g vampires are incredibly manoeuvrable, capable of leaping several meters from a standing start, but are they as agile on the ground? Riskin, Gerald Carter and John Hermanson headed to the island of Trinidad to test the vampires on terra firma (p. 1725).
Creeping along the ground, these tiny vampires feed on cattle after dark,so Riskin and his colleagues staked out ranches, successfully capturing 5 of the mammals ready for their track tests. Returning to the lab, Riskin introduced the bats to the treadmill and was amazed at how quickly they took to crawling on it. Having filmed the animals as they walked, the team found that the tiny creatures walked the same way as any other quadrupedal creature.
Once the bats were confident on the treadmill, the team turned the speed up and were amazed when the vampires burst into a strange bounding run with a top speed of over 1.1 m s–1. They pushed off from the ground with their mighty forelimbs bringing the hindlimbs foreword while in the air. Returning to the ground on their hindlimbs, the bats reached forward with their forelimbs ready to give the ground another shove. `It looks like a running push up' says Riskin.
The vampires had come up with an unusual approach to terrestrial locomotion, but were they unique? Riskin thought they might be until Bill Schutt suggested he take a look at the endangered New Zealand short tailed bat. Having evolved for millions of years free from predators, these tiny bats are equally at home on the ground and in the air. But how would their walk compare with the vampires'?
Teaming up with Stuart Parsons, Riskin and Schutt headed to a remote corner of New Zealand's South Island to put the bats through their paces. But the New Zealanders weren't as cooperative as the vampire bats. Although they were much friendlier, it took them significantly longer to get to grips with the moving treadmill. Once they had coaxed the New Zealand bats to start moving, the team could see that their walk was very similar to the vampire bat's, but even at their top speed, they never appeared to break into a run.
Knowing that walkers recover most of the energy from a pendulum-like stride, while the energetics of running are more like a bounce, the team decided to measure the forces exerted by the bats' feet as they moved across a force plate to see whether the tiny bats really were walking. Amazingly, the energetics were more like those of a bouncing run, even at the lowest speeds. The bats looked as if they were walking, but with a runner's energetics.
Riskin admits that he is surprised that the bats have solved the same problem in such different ways and adds that he hopes to continue working with these intriguing creatures. `There's a whole lot more out there to do' he says.