Statewide Acoustic Transects Help Biologists Monitor Bats on the Fly


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Statewide Acoustic Transects Help Biologists Monitor Bats on the Fly

Bat conservation interns Beth Oxford and Brannon Knight are hard at work this summer setting up acoustic monitoring transects for bats across the state. The Georgia Department of Natural Resources’ Nongame Conservation Section is following a nationwide survey protocol developed to help bat researchers across the country collect bat call data.

“Europeans have used acoustic transects to monitor bats for years,” said Trina Morris, a wildlife biologist for the Nongame Conservation Section. “Similar protocols have been used for monitoring birds and frogs in the U.S. but this is the first effort of its kind for bats.”

All of Georgia’s 16 species of bats use echolocation calls when flying for navigation and communication and while foraging for insects. Detectors pick up the echolocation calls of bats flying above the microphone, lower the call frequency within the range humans can detect and save a sonogram of calls that can be analyzed. Researchers often use acoustic monitoring in conjunction with other trapping methods to sample bats in an area.

Bat detectors may sound like an easy, non-invasive way to sample bats. The problem comes when trying to identify calls.

“Bat calls can be extremely variable and some species are almost impossible to distinguish based on call characteristics,” Morris said.

Analysis can require many hours in a lab measuring different call parameters and identifying each call individually. Most state and federal agencies don’t have the resources to analyze collections of bat calls.

As part of this nationwide survey effort, Eric Britzke of the Army Corps of Engineers Engineer Research and Development Center and Carl Herzog of New York State Department of Environmental Conservation have developed a protocol for establishing sampling routes used in monitoring bat populations. Britzke is also working to complete a computer program that automates call analysis, including species identification.

“Our hope is that by creating a sampling scheme that is easily to implement, land managers can have the information they need to assess impacts on bats populations, thereby directing conservation efforts to those species in the direst circumstances,” Britzke said.

The acoustic survey protocol allows comparisons of bat calls collected at the same transects, or paths, several times a year for multiple years. In Georgia, Anabat detectors are used to collect bat calls. An ideal survey route is 30 miles long and does not overlap or double back. Once a route is identified, driven and mapped, it’s time for a survey.

The protocol instructs surveyors to mount the detector on the roof of the vehicle, with the microphone Beth Oxford and Brannon Knightaimed straight up in the air. Surveys begin 30 minutes after sunset and should be completed in dry weather, when nighttime temperatures are above 50 degrees. Surveyors set up and turn on the Anabat, place it on top of the vehicle and drive the route at 20 mph. Afterward, calls are downloaded and stored for analysis. It is recommended that surveys be completed two or three times a year from June through August.

DNR interns Oxford and Knight (pictured) have spent several weeks this summer mapping out and running acoustic transects. “After many miles and hours of Annabatdriving Georgia highways, we’re pretty tired but encouraged knowing that we are taking part in this important process,” Knight said.

Oxford finds the Anabat work very interesting and plans to continue working with it for her senior thesis project. “This project will help us gain knowledge on bat populations and I think it is the next big step in bat conservation,” she said.

This is the initial year of the DNR project, though the U.S. Forest Service initiated several routes on national forests in Georgia last year. Most routes are being set up and may be sampled once this year. Next year, biologists hope to collect significantly more data with the help of several new bat detectors and statewide volunteers.

“We hope to turn this project into another successful citizen science project in Georgia,” Morris said.

She plans to use volunteers next summer to complete most routes across the state, similar to previous efforts to survey birds and frogs. “With the threat of white-nose syndrome so close to our state, people always ask what they can do for the bats. Here’s one way to help.”

White-nose syndrome, or WNS, which is named for the fungus Geomyces destructans on the muzzles and skin of affected bats, has spread steadily since being detected in New York in 2006. Now found in 13 states and Canada, it is estimated that more than 1 million bats have died from white-nose, including endangered species such as Indiana and gray bats.

Monitoring programs like the acoustic surveys are more important than ever, Morris said. In places like Georgia, where surveys are conducted before WNS is detected, the work will help biologists document any decline in bat populations. Hopefully, it will also help monitor survivors into the future.




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