Being a bat chasing prey, scientists say, is a bit like trying to hit a tennis ball under a strobe light.
That’s because bats track objects by echolocation – basically a type of sonar in which they generate high-frequency sounds and listen for the returning echoes. But they can’t click continuously, so all they get are acoustic snapshots.
Furthermore, they don’t beam these pulses out in all directions. Rather, scientists have found, they use their mouths to focus them into narrow beams, as little as 14 degrees across.
So how do they know where to “look” between pulses, in order to find prey that is attempting to flee?
The answer, says Angeles Salles, who did her research at Johns Hopkins University, Maryland, US, is that they think like skeet shooters, anticipating not only for the motion of their target but also for the speed of the shotgun blast (or in their case, the speed of sound) and “leading” their target by just the right amount to keep it in focus. All while doing this one pulse at a time.
“Imagine trying to catch a ball in a room only illuminated with a strobe light,” Salles said in late November, at the 181st meeting of the Acoustical Society of America.
To study this, her team placed bats on a platform and watched how they turned their heads to track moving objects that might be tasty treats. Slow-motion videos, she said, showed that the bats always aimed ahead of the target, automatically estimating where it would move from one pulse to the next.
To complicate the test, her group had the target change speed or direction, or even disappear behind a screen. The bats responded by emitting more frequent echolocation pulses, presumably in an effort not to lose track of it, but despite the fact that they now made more errors, she says, “they would still anticipate.”
In addition to filming how bats track their prey, she says, it’s also possible to monitor their brain activity with a device akin to a cochlear implant. Among other things, she says, this helps scientists determine how bats distinguish between their echolocation signals and acoustically very similar signals, called “frequency modulated bouts”, which are basically messages between bats: “Stay away from my food!”
“We found that there are different neurons in the brain that are selective for each of these, regardless of their acoustic similarities,” Salles says.
Such findings, she adds, aren’t just important to those studying bats. Other animals, particularly some marine mammals, also use echolocation, and the more we know about how bats do it, the better we will be able to understand them, as well.
There are also human applications. “Bats have brains that are very similar to humans,” she says. So, the more we understand about how they process sounds, the more we can learn about ourselves.
That, she says, can help with such diverse issues as understanding how we process language to understanding how visually impaired people can use sound in place of sight.