Seeing in the Dark

Acoustic monitoring technology allows researchers to hear bats’ echolocation signals.

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This story was originally published in the June 2018 issue of  Wonderful West Virginia. To subscribe, visit  wonderfulwv.com.

written by Carlee Lammers
photos courtesy of Allstar Ecology

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Is there anything better than a warm, dry, breezeless summer night? Not to the environmental scientists at Fairmont’s AllStar Ecology. These perfect nights allow them to capture clear, noiseless recordings of high-frequency sounds the human ear cannot hear—like bat echolocation.

For bats, these recordings could mean the difference between life or death. Biologists use them to help identify the presence of bats in a given area, crucial information for anyone looking to develop forested land without wiping out colonies of these important creatures of the night.

Hearing is Inaudible

As it turns out, there isn’t much truth behind the old idiom “as blind as a bat.” Bats can see quite well. Many scientists believe their vision is almost as good as—or in some cases, even better than—human eyesight. The misconception most likely stems from the species’ reliance on echolocation, a high-frequency biological system bats use for navigation at night.

Bats emit the high-frequency signals by using their larynxes to create pressure waves on the air. The waves propagate out through the air at a high velocity, hit against surfaces, then bounce back to the bats’ ears.

The animals use this echo to judge distances as they fly, giving them a kind of night vision that allows them to catch insects at night while avoiding predators. Echolocation gives bats a leg up on other insect-eating animals, says Ryan Ward, a senior environmental scientist and an owner of AllStar
Ecology. “Bats eat insects—well, birds also eat insects. Birds can’t see in the dark, but bats can,” Ward says. “They can exploit a time that other animals can’t exploit.”

To capture echolocation calls, AllStar Ecology relies on a weather-proofed recording device with a directional microphone, which biologists point at stands of trees they believe might house bats. Researchers are only permitted to use the monitoring systems from May to August when the bats have come out of their caves and are living in trees—bats spend summer months behind loose bark or inside hollow trees, reproducing and feeding their young. “They’ll form colonies,” Ward says.

Acoustic monitoring can be a lengthy process. Weather conditions have to be just right—no wind or rain for more than a 30-minute window of time—and surveys have to be conducted for multiple nights. “You can’t just go out for one night and be done,” Ward says. “Something could happen halfway through your night that precludes your night from counting.”

The researchers usually set the device to record from just before sunset until sunrise and specify which frequencies to record. When the machine recognizes a high-frequency sound, it kicks on and begins recording. That doesn’t always work out as planned. Once, Ward’s company set up its boxes during the day before conducting an acoustic survey later that night, not
realizing there would be an event at a nearby dirt bike racing track. The devices picked up the noise from the track throughout the night, rendering the audio they collected useless.

When the recordings are right, however, biologists can learn a lot from the sounds they pick up. “We can tell if bats are commuting through an area or are actually feeding in an area. We can get a sense of relative abundance,” says John Chenger, founder and president of the Pennsylvania-based Bat Conservation and Management, Inc.

Researchers use specialized software to sort through tens of thousands of recordings. Since each bat species has a unique call, the software can identify what kinds of bats are present in an area.

The computer analysis is not perfect, because some bat calls are so similar the software cannot tell them apart. “You’re seeing what they are closest to and matching what you’re recording to what’s been known,” Chenger says. “It gives you a probability. ‘There’s a 99 percent probability that this is this type of bat.’ While the analysis software helps point us in the right direction of what recordings may be of a particular species, all the species need to be
manually reviewed by a human to make the final call,” he says.

Lending an Ear

Bats are an important part of their ecosystems, providing invaluable insect control. Some bats are capable of consuming several thousand bugs in just one night. Yet many species are on the decline.

Four species of protected or endangered bats have been caught in West Virginia: the Indiana bat, the northern long-eared bat, the Virginia big-eared bat, and the gray bat. The Indiana bat has been on the endangered species list since the 1960s, while the northern long-eared bat was listed as “threatened” in 2015. “That triggered a lot of studies, because we actually have a pretty strong population of that here in West Virginia,” Ward says. “We have one of the few strongholds of the bat left in the northeast.”

The Virginia big-eared bat, which lives in mountainous areas in the eastern part of the state including the Monongahela National Forest, is also protected but, since it lives in caves yearround, the species is not affected when trees are removed. The gray bat is endangered, but is mostly
found in Tennessee and Kentucky—only one gray bat has ever been caught in West Virginia. Our state is also home to the eastern small-footed bat
and the tricolored bat, which are not yet listed as protected or endangered but are still considered to be rare.

This is why acoustic monitoring is important. Developers must be careful when clearing trees for projects, because removing a single colony could take 10 to 60 bats out of an ecosystem. Acoustic monitoring allows them to pinpoint whether a protected bat species is living in trees they hope to cut.

There is some data researchers cannot obtain through acoustic monitoring, though. Sound recordings are useless for measuring bat populations, since it’s impossible to know how many times a recorder picks up the same animal. The recordings also offer no information about the health of bats—a big issue for biologists as the fungal disease White Nose Syndrome has decimated bat populations in the United States over the past decade.

The only way to count bats, gauge the animals’ health, and tell for certain which species are living in a particular area is for biologists to see them with their own eyes. That’s why AllStar Ecology offers “mist netting” surveys, where researchers catch bats in thin netting suspended between two poles like a volleyball net. This method is laborintensive, requiring researchers to spend an entire night watching the nets. It also carries some risk—anyone conducting a net survey must have a rabies vaccination. To
help clients get the most out of their money, AllStar often uses acoustic monitoring in mist netting surveys, because it helps them set their nets up in the areas where they’ll catch the most bats.

It’s a little ironic: The same nocturnal behaviors that help bats find food and avoid predators make it difficult for humans to protect these crucial critters. It’s also humbling that, to keep up with a “blind” animal, humans must rely on loads of fancy technology and brain power. And even then,
researchers’ best efforts can be thwarted by the slightest change in the weather.

So the next time you’re out enjoying a warm, breezeless summer night,
spare a thought for Ward and his colleagues. Somewhere, they’re out waiting and listening, trying to protect animals that affect all our lives, even if we hardly ever see them.