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Seeing the bats through the trees

December 09, 2021

Experimenting with new tech in field surveys may help wildlife and wind farms live in harmony

On a July morning, a half hour before dawn, I stood along a rural Missouri road and worked the controls of a drone as it hummed across a dewy soybean field.

Mounted on the drone was a thermal infrared sensor, capable of picking up the heat signatures of animals on the landscape. In this mixture of Midwestern agriculture lands and woodlots, there are a lot of animals that can show up on the heat-seeking sensor—such as a grazing whitetail deer, for instance. But on this morning, I was looking for something small and tucked under the bark of a dead hickory tree.

I knew that the heat signature of Myotis sodalis, or Indiana bat, wouldn’t be large on my screen. But with a little luck, there would be a lot of Indiana bats—maybe two dozen or more—nestled in the tree and the heat signature would tell me that I had perhaps located a maternity tree for the federally endangered species.

I’ve conducted hundreds of wildlife surveys, and they have always been arduous and time intensive.  A statistically sound field survey can take several weeks and a half-dozen skilled biologists to conduct. I’ve always wondered: What if modern technologies could shorten time and reduce trips into the field?

My morning in the Missouri field was an experiment to see if my drone-mounted, infrared sensor could lead to safer, faster, and more accurate ways to survey and collect information for bats and other animals.

Indiana bats (left) show up as bright splotches on a dead tree (top right) when detected by a heat-seeking, infrared sensor on a drone. Bottom right, the same tree in daylight.

When bats and turbines collide

I’ve been thinking about how to use modern technologies for bat surveys here in Missouri, where the construction of wind turbines has been increasing and we have populations of endangered Indiana bats.

My work lately has focused on helping wind-farm operators reduce impacts on bats. Not surprisingly, my fascination with bats goes back to childhood and continued through college. My mom recently discovered a “report” I did on bats as a kindergartener. As a master’s degree student at Antioch University, I spent a great deal of time driving the roads of New England in an aging Subaru Forster outfitted with a GPS unit and a sensitive bat-detecting microphone mounted to the roof.

My master’s degree work was to identify bat species and predict their locations using a 3D overlay of forest structure created by LiDAR. As a wildlife biologist, I am always motivated to discover how technologies from varying disciplines can be employed to answer ecological questions or to improve older methods of data collection.

My morning in the Missouri field was an experiment to see if my drone-mounted, infrared sensor could lead to safer, faster, and more accurate ways to survey and collect information for bats and other animals.

Lately, Stantec has been doing a lot of bat surveys for wind developers. Wind development plays an instrumental role in combating climate change, which is a global phenomenon that can and will affect wildlife in unforeseeable ways. While it is important to continue developing renewable energy, it is also important to monitor and mitigate local wildlife impacts, particularly on threatened and endangered species like the Indiana bat.

Bat collisions with turbine blades is a problem. Also, when a wind developer wants to clear trees inside the range of a protected bat species, they need to document the presence or absence of those species and minimize impacts where possible. Our teams conduct bat surveys so we can help our clients avoid any unanticipated impacts.

Wildlife surveys help determine the presence or absence of bats during development of wind farms.

Bringing bat surveys into the 21st century

However, bat surveys are especially labor-intensive and use a five-part process to identify species, population abundance, and maternity roosts. This field work involves:

  • Identifying potential bat habitat
  • Setting up fine-mesh “mist” nets to capture bats
  • Identifying species
  • Outfitting them with tiny, very high frequency (VHF) tracking devices that are attached to their backs
  • Tracking them to their roosts.

Tracking the bats is done with an antenna and VHF receiver—most definitely 20th century technology! Once the bats’ general location is determined, we head out at dusk to visit the roost and count the bats as they emerge for their nightly foraging.

My experiment using a drone-mounted thermal camera to identify maternity trees was my effort to apply technology from the 21st century to solve an ecological challenge. My thought was that, in the early morning, bats will generate more heat than the trees, so areas where bats are roosting would be easier to identify using thermal imagery.

When I flew the drone across the soybean field, we were testing this technology on a tree I knew to have bats. When viewed up close with the drone and infrared camera, the locations where bats were roosting underneath the sloughing bark were easy to see. A bright thermal signature appeared on the tree, even though the bats were under the bark.

The experiment proved that we could locate bats on a tree with a drone and infrared-sensing device. However, the bat-locating technique is still evolving. For instance, large living trees maintain their heat throughout the night, which makes this type of survey more challenging as living trees stand out more readily in thermal imagery. The tree that I monitored that morning turned out to be dead, which made the bat heat signature more apparent.

But after I flew the drone past the tree in the morning, I returned that night and sat underneath the same tree and counted more than 140 Indiana bats flying out from under the bark. The bats flew off into the Missouri night to feed on insects, one of the many benefits bats provide to the ecosystem.

As the world moves toward a low-carbon economy, there is an increase demand for renewable power. That power generation can have impacts on wildlife. These methods we’re exploring to improve our existing surveys will help our clients do their best job to protect endangered species from negative impacts while generating clean energy in the face of climate change.

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