Some species can eat more than 70 percent of their body weight in insects per night. One little brown bat can eat up to 1,000 insects in a single hour, according to the U.S. Beurea of Land Management. But that number of insects being eaten by bats is dwindling.
For example, one million little brown bats that have already died from the disease could have eaten between 660 and 1,320 metric tons of insects in one year, according to the U.S. Bureau of Land Management.
“The disease has progressed faster than I thought it would,” said Loeb. “It’s only going to get worse and continue to spread until a treatment or cure is found. But we’re continuing to work here on campus and with our partners to understand the spread of this deadly disease and to minimize its impacts.”
Loeb is working alongside several Clemson University researchers, including Sirajuddin, to understand how the massive bat die-off is altering ecosystems and the structure of bat communities across the Southeast. That team also includes Clemson wildlife biologist David Jachowski and wildlife biology graduate students Katie Teets and Ben Neece.
Together, with an array of federal and state collaborators, the bat researchers are using radio transmitters and acoustic technologies to conduct studies that could have implications for the future management of bats.
A Blueprint for Conservation
The researchers’ efforts are rooted in the life work of Loeb, who has become one of the leading bat researchers in the Southeast. “Her work throughout has established a lot of the basic ecological information we have about bats in the Southeast. I don’t think our projects could have happened without her,” said Sirajuddin.
Loeb graduated from the University of California – Davis in 1987 with a doctorate degree in ecology and joined the U.S. Forest Service’s Southern Research Station in Asheville, N.C.
She was then assigned to the Upland Hardwoods Research Unit and located to Clemson University, where she later became an adjunct professor. Throughout the 1990s, Loeb studied flying squirrels and red cockaded woodpeckers. But then the Forest Service redirected her to bats in 1999. Since then, Loeb has devoted her career to answering questions about bat ecology and conservation.
U.S. Forest Service research ecologist Susan Loeb
But she’s also worked to minimize the effects of white-nose syndrome.
No one knows for sure how the disease arrived in North America. Though a recent study by the Royal Veterinary College suggest that the disease as brought over from Europe by humans.
The disease was first detected in New York State in 2007. It has since spread throughout 31 states, including South Carolina, and five Canadian provinces.
In 2007, Loeb started catching bats in northwestern South Carolina and Georgia in order to collect data before the disease began to decimate bat populations across the Southeast. “I knew we’d need that data some day,” said Loeb. “I’m just glad we collected it. Because it allowed us to see those declines.”
Loeb partnered with scientists from the National Park Service, U.S. Fish and Wildlife Service, U.S. Geological Survey, Canadian Wildlife Service and other wildlife and conservation groups to create the North American Bat Monitoring Program.
“With white-nose spreading, we needed a monitoring program that would allow agencies and researchers to document the impact on bat populations. So the goal was to develop a program that could identify priority species for conservation and measure the effectiveness of our actions to mitigate stressors,” Loeb said.
“There really wasn’t anything like it at the time," she added.
Eventually, Loeb published “A Plan for the North American Bat Monitoring Program,” providing the details that researchers and managers needed to start monitoring bat populations and contributing their survey results to a database.
The plan includes four approaches to gathering bat population data:
- Hibernaculum counts made of bat populations in caves and mines in winter;
- Counts of bats in maternity colonies in summer;
- Mobile acoustic surveys along road transects; and
- Acoustic surveys at stationary points.
The program allows researchers to input their data into a Bat Population Database. As data accumulates, the program will issue reports to biologists and managers that reveal trends in the abundance and distribution of North American bats. It will also release periodic reports focused on individual species that are threatened.
Thirty-one states and 10 Canadian provinces use the program.
In March 2015, Loeb was honored with the Forest Service’s “Wings Across the Americas Research Award” for her contributions to the North American Bat Monitoring Program.
She has since continued to research bats, develop conservation plans and coordinate recovery efforts across the Southeast.
The First Statewide Bat Population Study
One of those efforts is the Carolinas Acoustic Bat Survey.
Last spring, Loeb helped Neece secure funding from the U.S. Fish and Wildlife Service for the first statewide bat population study in South Carolina, which he is currently completing with help from SCDNR. “The goal is to find out more about bat distribution throughout the state,” Neece said.
For the past two summers, Neece has collected bat echolocation calls from more than 30 areas across the state. He selected the locations for habitat variety, bat species diversity and low clutter that would interfere with recording. Each summer, Neece started in the Lowcountry and worked his way up to the Upstate. Neece used stationary acoustic samples and mobile acoustic routes to detect the high-pitched frequencies emitted by the flying mammals as they capture bugs and navigate through the dark.
“Bats are notoriously difficult to study. They are active at night, can detect nets and traps, and are fairly secretive when roosting,” said Neece. “So the acoustic surveys really helped me effectively monitor these elusive animals.”
For the mobile acoustic routes, Neece had to drive in each area for two consecutive nights with a bat detector and stainless steel microphone attached to the cab of his green pick-up truck. He would then drive at least 20 mph in order to capture the echolocation calls accurately.
For the stationary surveys, Neece had to place several bat detectors at select spots within the survey areas for up to four nights at a time. The process had to be repeated in the same week each summer.
Neece completed the first phase of his study earlier this summer in Oconee County. Now, he is using classification software to help him identify the calls by species and abundance.
Clemson University graduate student Ben Neece attached a mobile bat detector on the hood of his truck and drove across the state in 2015 and 2016 to record bat echolocation calls. Photo by Clemson University.
North America has more than 150 bat species, 47 of them in the U.S.
“Many bat calls sound the same,” said Neece. “But there are subtle differences by species. The computer software helps me identify them visually since bat calls are at frequencies humans can’t hear.”
His analysis of the second survey should be done next spring. He will then turn over his data to SCDNR, where it will be uploaded to the database and used as the foundation of future North American Bat Monitoring Program efforts in the state.
“The goal is to establish these routes and perhaps add more routes in areas that haven’t been surveyed. It is wonderful that so many people have pulled together to make this happen. After we have the kinks worked out, this can provide a volunteer opportunity for citizen scientists,” Bunch said.
Neece recorded about 30,000 bat calls after noise-filtering technology cut insect sounds and ambient noise. He detected no tricolored bats in several areas of Oconee County.
Trouble for the Tricolored Bat
The tricolored bat has one of the highest mortality rates among bats affected by white-nose syndrome. Throughout areas of the Northeast, the mortality rate for tricolored bats has exceeded 98 percent, according to the Center for Biological Diversity.
“These bats tend to hibernate in the deepest parts of caves, where temperatures and humidity are highest, which are ideal growing conditions for the fungus that causes white-nose syndrome,” Loeb said.
She added that they also hibernate longer, which increases their exposure to the fungus.
In June, the Center for Biological Diversity and Defenders of Wildlife petitioned the U.S. Fish and Wildlife Service to protect the tricolored bat under the Endangered Species Act. The act currently protects the northern long-eared bat and could potentially protect the little brown bat, which is under consideration.
“The tricolored bat is in grave trouble, and it’s time the federal government took action to keep this species from tumbling off the cliff of extinction,” said Mollie Matteson, a senior scientist with the Center for Biological Diversity. “Among the three bats most devastated by white-nose syndrome, the tricolored bat has been virtually forgotten, but that can’t continue if this species is to survive.”
Sirajudden and Loeb received grants from the U.S. Fish and Wildlife Service and U.S. Forest Service last year to understand the vulnerability of tricolored bats to white-nose syndrome in the South. They plan to test whether the skin temperature of tricolored bats during hibernation is within the range for the growth of the fungus Pseudogymnoascus destructans, which causes white-nose syndrome.
Sirrajuddin (left) and Loeb (right) put on their white Tyvek suits, which help prevent the spread of WNS.
Pseudogymnoascus destructans grows in caves with a temperature range of 39 degrees to 59 degrees Fahrenheit, according to a study in the Journal of Applied and Environmental Microbiology. South Carolina caves typically range between 50 degrees to 58 degrees Fahrenheit, according to the U.S. Beurea of Land Management.
Sirajuddin and Loeb will be studying a cave not far from Clemson University that has suffered a major population decline. Its tricolored bat community has been reduced from 321 individuals in 2014 to 67 individuals in 2016, according to Sirajuddin.
In late November, the researchers will dress head-to-toe in white Tyvek suits and venture head first into the darkness with their headlamps. With surgical precision, they will affix small temperature-sensitive radio transmitters to tricolored bats, which are about as small as a wine cork. A nearby radio receiver and data logger will record torpor temperature and duration as well as arousal temperature and duration.
Torpor is the state of decreased physiological activity in hibernating animals. It results in reduced body temperature and metabolic rate. The duo is trying to understand how these patterns make bats more susceptible to white-nose syndrome.
In North America, cave-dwelling bats that hibernate in groups contract the fungus from other bats that have already been infected, often when spores lands on their wings. The fungus then spreads throughout the bat’s body, causing a white growth to form on its nose and wings, according to Sirajuddin.
The disease causes bats to wake up more often during the winter. “The increased waking from torpor is using up their fat stores during a time of year when there are not a lot of insects for them to eat,” Sirajuddin said.
Bats with white-nose syndrome exhibit unusual behavior, including flying outside during the day and clustering near the entrances of caves and mines. The increased activity and lack of food leads to starvation and death. The fungus can also produce lesions on the delicate skin of the wings, disrupting flight and causing dehydration.