Ears in the Field

Ultrasonic recorders help researchers detect bats remotely

by Melody Schreiber

On their first night in Rwanda, the Bat Conservation International (BCI) field research team got lucky in an unexpected way. They had set up nets in Nyungwe National Park, one of the oldest rainforests on the African continent, to try to catch the critically endangered Hill’s Horseshoe Bat (Rhinolophus hilli), which has not been seen since 1981. But instead of catching that rare bat, they caught another—the Damara Woolly Bat (Kerivoula argentata)—which had never been caught in Rwanda before.

They were able to record the newly confirmed bat’s echolocation call, which means they can now detect it by sound without needing to catch it again. They used an ultrasonic recorder from Wildlife Acoustics, a Massachusetts-based company specializing in bat and bird acoustic equipment, to record the call.

Recording and tracking bats with acoustic equipment can be a less intrusive and less resource-intensive way to monitor bats, particularly from a distance. The equipment can be pointed at the sky to record and identify bats, but it can also be stationed in remote locations for long periods of time. The recorders run on batteries and can be programmed to run from sunset to sunrise.

In Rwanda, for instance, park rangers trekked for about a day and a half to position recorders at the entrance to a remote cave. The recordings showed the bats in the cave were not the Hill’s Horseshoe Bat, freeing up the researchers to spend their valuable time focusing elsewhere.

Acoustic monitoring projects are being used to detect the Jamaican Flower bat (Phyllonycteris aphylla) and the Jamaican Greater Funnel-eared Bat (Natalus jamaicensis), the Fijian Free-tailed Bat (Chaerephon bregullae), and the Florida Bonneted Bat (Eumops floridanus), the rarest bat in the United States. The Florida project uses 16 recorders to form an acoustic monitoring grid to track the federally endangered bat through changing seasons, food sources, and roosts.

Sherwood Snyder, director of product management at Wildlife Acoustics, says it would be “excruciatingly expensive” and time-consuming for bat biologists to do that level of work every day across multiple locations. “It would take an army of bat biologists to match that,” Snyder says. Instead, the equipment frees up researchers to focus on the most important work at hand, and it also allows them to monitor from a distance, which is especially helpful during a pandemic.

“Twenty years ago, this just wouldn’t have been possible,” says BCI Director of Endangered Species Interventions Dr. Jon Flanders. “The equipment was far too expensive, far too heavy; you weren’t able to stick it out for days on end. Whereas now, it’s waterproof, it’s robust, it’s really easy to use. So, the rangers are able to stick it in their backpack and take it on part of their normal duties.”

But recording bat calls isn’t just for bat biologists anymore. Less expensive, consumer-focused ultrasonic sensors are also available to translate echolocation calls to a human audible range and then create a spectrogram, suggest a species from a database of bat calls, and even show a little photograph of the identified bats.

BCI Chief of Strategic Partnerships Mylea Bayless says that equipment like this has great potential for involving community scientists and naturalists on Bat Walks, hosted by guides with acoustic detectors.

“It’s an opportunity for conservation involving community contributions to science, and because the detectors are so accessible, they also present unique opportunities for outreach and for giving people an in-person introduction to bats through nature walks,” Bayless says.