Sonar wars in the night skies

William Conner never expected to ride around Winston-Salem in a cherry picker on the prowl for bats. Truth be told, he's more of a moth kind of guy.

But after the Wake Forest University professor of biology spent 10 years unsuccessfully nudging his students to study how moths and bats acoustically communicate, he took matters into his own hands.

Now, he not only has a bat house under the eave of his two-story home, he's launching a project to teach local children about acoustics and was the first to discover a new strategy some moths have evolved to fend off bat predators.

It all began 10 years ago, midway through his lecture in an animal behavior class where Conner was privy to a eureka moment.

"I realized during a lecture that I had a way of testing them (bats and moths), which turned into my current study," said Conner, referring to the equipment and lab techniques he uses. Before then, he spent his career studying moths.

When the idea struck him, he had already spent a decade studying moths' sound-producing structures, called tymbal organs, and how moths use sound to communicate with one another in courtship. From there, it was natural to ease into moths' communication with their predators.

Conner began to study bats and moths together and learned that just like military aircraft, at least one species of tiger moth can jam enemy sonar by producing a sound at the right frequency. Moths, of course, found it first.

Jamming sonar means the moths interfere with their enemies' fine-tuned way of bouncing sound off objects to navigate. However, the b. trigona moth seems to thwart its enemy, the bat, every time, and the military still can't claim that rate for foiling anti-aircraft missiles. Conner has only studied the one type of moth but has never seen a moth get eaten after producing the high frequency racket. So, can the military learn a thing or two from a moth?

Maybe so, says Conner. He and graduate student Aaron Corcoran study how the signals produced by bats and moths have evolved, and by turns eclipsed each other, throughout their predator/prey history. For now, this steely grey tiger moth - dappled with orange to befit its name - has the advantage. While the military toys with one frequency or another in electronic jamming, the tiger moth easily sounds just the right frequency or mix of frequencies to avoid the bat's jaws.

"This is the first incidence of prey jamming a predator's sonar," said Corcoran. "There are a number of parallels to human military strategies. These animals have likely been using this strategy for millions of years, predating human technologies." The study was published recently in the journal Science.

After time spent in Wake Forest University bat facilities, the team has determined that the moth isn't simply warning the bat away or startling the bat out of a meal. No, they think the moth's distinctive ultrasonic clicking, which sounds to the human ear like the quick back-and-forth wiggling of a zipper, causes the bat to hear double or interrupted echoes when trying to locate prey. Ultimately, this means miscalculating the moth's location and losing the snack. But the team still really doesn't know how the clicking works.

Steve Nowicki, a Duke University animal communication expert who is not involved in the study, says that grasping how conversation systems work within and without a species, from the inch-long tiger moth to the flat-faced bat, is important for more than military technology.

"Communication is fundamentally a biological problem. By understanding how animals communicate, we might get some glimpses into the origin of our own language and therefore what it means to be human," Nowicki said. In their lab studies, Conner and Corcoran dangled different species of live moths from the ceiling with fishing line, then allowed bats to fly laps, so the scientists could observe the predator/prey dance. Soon they found that when the bat neared a tethered tiger moth, the moth rapidly began clicking, causing the bat to miss his intended meal. In their indoor facility at Wake Forest, which with its ceiling-to-floor foam walls looks more like a recording studio than a science lab, team members capture the entire interaction with a high speed video camera and high frequency microphone. After studying their findings, all data signaled that the moths were, indeed, jamming the bat's sonar.

To maintain an unbiased study, Conner needed bats that had never been exposed to prey and, thus, had never encountered a clicking moth. So he called exterminators around Winston-Salem who were only too happy to point out bat infestations. The unlikely scientist and exterminator team rode around in a cherry picker to capture young bats all over the city. These juvenile bats haven't flown yet, and thus haven't encountered flying moths.

Conner, who says everyone always seems to have a strange bat story to tell him, hopes next year he can add bats from a roost under his home to the research lab.

Though the researchers know that the b. trigona moth thwarts bats' echo-location cries, they want to test their theory in the wild in case bats have different ways of maneuvering in a space bigger than the Wake Forest laboratory flight room. For his doctoral work, Corcoran will continue the lab's studies at the Southwestern Research Station operated by the American Museum of Natural History, tucked away in an Arizona canyon. Here, 30 moth species, including b. trigona, live, along with 18 species of bats, a sizable step up from the two species at the Wake Forest "bat cave." Corcoran will lure moths to a central spot with a black light, then use video and audio recording techniques similar to his lab to see how bats interact with the moths in a natural setting.

"The more we look at different species of moths and bats, the more likely we'll discover novel mechanisms of interaction between predator and prey," said Conner. "Our goal is to understand the evolution of acoustic strategies."

The main aim may be scientific understanding, but Conner hardly remains cooped up in the lab. As a part of his $185,000 grant from the National Science Foundation, Conner became part of a larger science K-12 teaching initiative and plans on building a bat house to teach local children about acoustics. Once approved, the lab will erect a large wooden bat house this summer at the SciWorks science center in Winston-Salem. The house's population, capable of holding 3,000 furry inhabitants, will gradually diminish as Conner releases bats into the night as a grand finale to his outside amphitheatre presentations.

"By studying how bat hearing works, you're indirectly studying how human hearing works at the same time," Conner said. "It's great to use our research to teach children how they use their ears to locate sounds."

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