Every summer evening 1.5 million bats emerge from underneath the Congress Avenue Bridge in Austin, Texas, on a search for their favorite meals of mosquitoes and other insects. To track their tiny flying prey（猎物）, the bats make high-pitched（声调高的）sounds that deflect from an insect back to the bats’ large ears. The information from this process of echolocation（回声定位）tells the flying mammals the precise path of their fast-moving food. But how does any single bat in a crowd of thousands know that the ping it registers is not some other bats’ echo? Navigating this potential interference is not only the province of bats, however. Dolphins and other animals that rely on echolocation must also find ways around the maze of found waves around them.
People want to figure out how bats and dolphins do it because these animals are what Laura Kloepper, an assistant professor of biology at Saint Mary’s College in Indiana, calls “bio-inspiration” — helping us to find technological solutions to problems in our everyday life. The built-in biology of an echolocating bat holds secrets that would help human researchers develop better “active sensing” devices that imitate what bats do.
Kloepper highlighted the power of bats’ active sensing abilities in a presentation at the 176th meeting of the Acoustical Society of America that compared them with the powerful echolocating capabilities of dolphins. In her talk, Kloepper told of how her research group attacked a pair of dolphins with artificial dolphin-like clicks to try to confound them as they chose between two options. Her team challenged the marine mammals by pulling tricks such as adjusting the angle of speakers making the sounds to confuse them as they homed in on their targets of choice. What the humans learned was dolphins use two possible strategies to block out the nonsense noise. They either change the frequency of their calls — to a higher or lower pitch — or they change the timing. Either adjustment gives a dolphin a personal call, a signature it can recognize.
Kloepper has, of course, also studied bats. For this research she uses what she calls a “biological drone（生物无人机）”, a trained Harris’s hawk named Belle. Armed with a tiny camera and microphone, Belle wings into the midst of bat crowds and records their many calls for the sake of science. Kloepper says the reason she uses hawks, besides the fact “hawks are super-cool”, is that sending a regular drone with spinning propellers（推进器）into a dense bat crowd “wouldn’t be ideal.” Her team does use drones during night crowds, when the bats fly at greater distances from on another and are less likely to run into the machine.
A dolphin’s click is about a 20th the duration of a bat’s call. This difference, Kloepper says, leaves bats better able to make adjustments to their calls. Whereas a dolphin might change pitch, a bat has a slightly more nuanced repertoire（微妙的技能）to deal with the jamming. “Dolphins make impulsive signals that sound like clicks — sort of if you snapped your fingers together,” Kloepper says — whereas bat calls are more like human whistling. “Sure, we could slightly change some of the characteristics of our fingers snapping,” She notes, “but you could make your whistle go up or down in pitch or even jump between pitches, and you can control how long your whistle is.” Bats show a similar level of fine control over their echolocation, she says.
But the mystery of how bats pull off this jamming countermeasure remains. Researchers’ next step in solving this challenge is to focus on individual bats and their calls. Kloepper predicts “new electronic hardware to go on our drone and hawk that will allow us to really home in on which bat is making which call when it’s in the middle of this massive group.” The dolphins are not left out either. Kloepper plans to expand on her work by challenging the chatty marine mammals with even more interference to see if they can still echolocate.