Media & Education
BATS Magazine

Volume 39, Issue 1, 2020

Fly Through the Caves

LiDAR imaging technology helps scientists protect bats

By Katarina Zimmer


After bat conservationists feared Jamaican flower bats (Phyllonycteris aphylla) were extinct for decades, it was a welcome surprise for researchers to discover a small colony of silky, blonde bats roosting in a cave in eastern Jamaica in 2010. But the joyous occasion was tainted with concern about the future stability of the underground cave, which could be the only remaining refuge for the species.

The cave lies in the middle of a suburban area. Not only is it close to homes—which could possibly have leaky septic tanks, allowing fluid to seep through the porous walls of the cave, destabilizing the structure—but it’s also fringed by a busy road, which would exert undue stress on anything beneath. Collapse of any part of the cave would spell disaster for the bats roosting in the crowded chambers below, threatening not only the 250-strong population of Jamaican flower bats, but also other species living there.

In order to help Jamaica’s National Environment and Planning Agency (NEPA) craft long-term management plans for the cave, BCI experts needed to know how vulnerable the cave was to damage caused by the infrastructure surrounding it. They needed to know where nearby dwellings and the road were in relation to the cave. Were they directly above, threatening to cause a collapse at any moment, or were the bats inside safe?

Thankfully, BCI experts have a tool to help them answer that question: a handheld 3D scanner based on LiDAR (Light Detection and Ranging) technology. The device emits rapid laser pulses—43,000 per second—and measures the distance they travel before they bounce off the walls of the cave and return to the scanner. This creates a 3D “point cloud” that recreates the cave’s inner structure and the above-ground surface.

In under two hours, Jason Corbett, BCI’s director of habitat protection and restoration—a seasoned surveyor of bat caves—clambered through the cave with the 10 x 5 x 5-inch device in hand, scanning the cave one section at a time. Before access to a tool like LiDAR, surveying the cave would have taken days. Priyesh Patel, BCI’s geospatial products and data manager, then used a computer program to stitch together the scans, generating a complete 3D map of the cave’s entrance and interior, showing it in relation to the road and nearby dwellings.

“From that, we were able to tell that the road goes right over the top of the cave,” Corbett says. That knowledge will allow BCI experts to write up a management plan to ensure NEPA is consulted before any roadwork is undertaken, and road crews would know to stop drilling at a certain depth.

Corbett has since mapped around 20 other caves, including the Nakanacagi Cave in Fiji, home to the only known maternity colony of Fijian free-tailed bats (Chaerephon bregullae). The handheld LiDAR scanner has “been a game changer,” according to Dr. Jon Flanders, who directs BCI’s endangered species intervention program. Without the device, mappers would have to spend days tracking the cave’s circumference with a compass and line, or set up tripods with stationary LiDAR scanners throughout the cave—making it practically impossible not to disturb the bat roosts.

Now that the hand-held scanner has proven successful, BCI hopes to apply this technology to more caves harboring endangered species to visualize complicated cave structures and better understand habitat needs and aid restoration planning, explains Kevin Pierson, BCI’s chief conservation officer. “It’s becoming a default part of cave conservation for us,” he says.

 

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