Nature Conservancy Confirms Bat Visitors at Artificial Cave
Recordings of bat calls captured.
Nashville, TN | June 21, 2013
In early October 2012, The Nature Conservancy put the finishing touches on a daring gamble to save America’s bats from the epidemic of White Nose Syndrome (WNS). Based on data from the first year’s operation, that gamble is paying off.
The nonprofit organization’s Tennessee Chapter spent some $300,000 to build an artificial cave prototype as an alternative habitat for bats during winter hibernation—when they are most vulnerable to the deadly fungus that causes WNS. Since 2006, WNS has killed more than 6 million bats across the eastern United States and Canada.
Initial indications are that the artificial cave is off to a good start and functioning well. Bats visited the cave, even though it was completed after their hibernation season had already begun. In addition, the Conservancy was able to attain the ambient temperature and humidity levels in the artificial cave during the winter that are critical to the bats’ use of the environment.
Gray bats, the most prevalent species at the nearby natural cave, prefer very cold, humid conditions for hibernation. Temperature and humidity data loggers confirm that the artificial cave was a few degrees colder than the natural cave (Bellamy Cave), which is actually closer to the gray bats’ preferred hibernation temperatures. The artificial cave’s humidity fluctuated a bit more than the natural cave, so more work will be done this summer to ensure stable humidity for next winter.
Because the artificial cave needed to be kept dark and free from human visitation, a key component of the project was bioacoustics monitoring equipment donated to The Nature Conservancy specifically for the artificial cave by Wildlife Acoustics. The Massachusetts-based technology company, a leading developer of recording units for the calls of birds, land animals and marine life, donated two units developed to record bat calls at the artificial cave site.
The Nature Conservancy installed One Song Meter SM2BAT+ unit at the natural cave site on the property to record bats’ ultra-sonic (high frequency) calls. “We recorded fall swarming calls at the natural cave so that we could re-broadcast them at the artificial cave to attract bats to it,” explains Cory Holliday, director of the Tennessee Cave Program from The Nature Conservancy. The idea was to lure bats to the new structure.
The second recording unit was installed at the artificial cave to capture the calls of bats in the man-made structure. The plan appears to have worked well. Wildlife Acoustics performed an analysis of audio recording data captured at the artificial cave with its new Kaleidoscope bat software. The digital recordings confirm that bats of more than one species regularly visited and explored the structure between October 2012 and February 2013.
“Using the Wildlife Acoustics units, we were able to detect repeated bat activity at the artificial cave with great regularity throughout the winter, which confirmed that bats had found the artificial cave,” says Holliday. “We had a lot of configuration and performance issues with the video cameras being used in the artificial cave. Fortunately, the acoustic data gave us a high level of detail about bat activity inside the artificial cave during its first winter in the ground. We would not have known just how much bat activity we had at the artificial cave without Wildlife Acoustics’ units.”
Because the infrared and thermal video cameras installed in the artificial cave did not function well, it is difficult to determine how many bats actually took up winter residence in the cave. However, Holliday found evidence that suggests at least two bats spent at least part of the winter there.
“It is encouraging that fair numbers of bats were checking out the site,” says eminent bat expert Merlin Tuttle. “We have little information on how long it takes to attract major hibernating populations. Since this site is near Bellamy Cave, the odds of early success should be above average. Pioneering isn't easy, but progress depends on it.
“Our goal for Year One was that we wanted our artificial cave to maintain a temperature range close to that of the natural cave,” says Holliday. “We achieved that. We did not have any expectations for bats visiting the cave this first year. We ended up having a lot more bats entering and exiting the structure than we had expected, which we know from the Wildlife Acoustics recordings. We are very hopeful that we will see more bat activity this winter.”
The Nature Conservancy will spend this summer working to fine-tune the artificial cave to make it even more attractive to bats before the fall when they begin seeking caves to hibernate.
The Nature Conservancy is a leading conservation organization working around the world to conserve the lands and waters on which all life depends. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at www.nature.org