Clemson researchers lead national effort to conserve imperiled bat populations
CLEMSON — A team of Clemson University scientists is on the forefront of a national effort to understand how a massive bat die-off is shifting the structure of bat communities and altering fragile ecosystems.
Six million to eight million bats have died across North America since 2006. Habitat encroachment and changing climate are playing a role in their demise, but a deadly fungal disease called white-nose syndrome is the major contributor to a stunning and tragic loss of bat life that could have major implications for crop pest management and ecosystem health.
The research is being conducted by Clemson wildlife biologist David Jachowski; U.S. Forest Service research ecologist Susan Loeb; and Clemson wildlife biology graduate students Pallavi Sirajuddin, Katie Teets and Ben Neece.
Together with an array of federal, state and private collaborators, the Clemson team is using radio transmitters and acoustic technology to conduct research with broad implications for the future management of an imperiled species that plays an important role in insect and pest control; pollination and seed dispersal; soil fertility and nutrient distribution; and as prey for higher-level predators, such as owls, hawks, raccoons and snakes.
White-nose syndrome on the march
Imagine every few hours, night after night, an unknown irritant wakes you from your sound sleep. Imagine how this would affect your physical and mental health and how disorienting it would be. It could even eventually kill you.
This is what happens to bats with white-nose syndrome. The fungus that causes white-nose syndrome causes the bats to rouse more frequently from their state of hibernation, causing them to use up their fat reserves long before the winter is over. Eventually, the bats just starve to death.
The first cases of white-nose syndrome were found in bats in 2006 near Albany, New York. Since then, the disease has marched rapidly across 28 states and five Canadian provinces.
White-nose syndrome is believed to have been brought to North America from Europe. It only affects bats that hibernate in cold caves and similar structures, such as mines and tunnels, called hibernacula. Seven bat species, including three that are on the federal endangered species list, have been affected by the disease. White-nose typically kills 70 percent to 90 percent of bats in an infected hibernaculum. Cases of 100 percent mortality have been found.
Until recently, the disease had only affected bats in the Eastern U.S., but on March 11, a group of hikers near Seattle found a dying bat. The U.S. Geological Survey Wildlife Health Center examined it and made the alarming confirmation that white-nose syndrome had crept inexorably into the Western U.S.
It was first found in South Carolina in 2013.
Not far from the Clemson campus, in a cave in northwestern South Carolina, one community of tricolored bats has seen its population numbers plummet from 321 individuals in 2014 to just 67 in 2016, according to graduate student Pallavi Sirajuddin.
In the fall, when the bats are hibernating, Sirajuddin, dressed head-to-toe in Tyvek, enters their cave. With surgical glue and surgical precision, she affixes tiny temperature-sensitive radio transmitters to bats about the size and weight of a wine cork. A nearby radio receiver and data logger records torpor temperature and duration and arousal temperature and duration.
Torpor is the state of decreased physiological activity in hibernating animals. It is characterized by reduced body temperature and metabolic rate.
Sirajuddin is trying to understand how these patterns make the bats more susceptible to the deadly disease. She will compare her findings to a healthy bat community in Mississippi.
“This 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.
The fungus can also produce lesions on the delicate skin of the wings, disrupting flight and causing dehydration.
And here’s the scariest part: Research suggests that Pseudogymnoascus destrucans, the aptly named fungus that causes white-nose syndrome, thrives in 50-58 degrees Fahrenheit, the temperature range of many caves in South Carolina and the Southeast.
Comparing bat populations before and after white-nose syndrome
From 2003 to 2011, Jachowski and colleagues at Virginia Tech led a study of bats in Upstate New York that was published in the journal Diversity and Distributions.
The study spanned the time immediately prior to and following when white-nose syndrome first appeared in the region, and the researchers found that before the disease outbreak, the species of bat known as the little brown bat was five to 53 times more active than all other bat species, and that little brown bats were consistently detected during evening hours.
Following the arrival of white-nose syndrome in 2006, little brown bats and other cave-roosting bat species have been decimated. Results from the New York study suggest that the direct die-off of these important insectivores not only is alarming, but that other bat species not directly impacted by the disease are shifting their behaviors in response to the less-occupied night skies.
“There’s evidence that the presence of high numbers of certain bat species can suppress other bat species through competition, but we don’t know a lot about the effect of bat species decline on the overall structure of bat communities. Essentially, we are seeing a reshuffling of where and when remnant bat communities are using the landscape. It appears that areas formerly dominated by little brown bats are being made available to other, historically imperiled bat species,” Jachowski said.
Jachowski believes that this “reshuffling” could have major implications for how biologists and land managers try to identify areas to protect and conserve these vulnerable remaining populations.
In a newly initiated project funded by a grant from the U.S. Department of Interior, Teets, a graduate student in Jachowski’s lab, will spend the summer using acoustic devices that record bats’ echolocation calls to monitor bat populations at sites in South Carolina and Georgia while researchers from Virginia will collect data from sites in New England and the Mid-Atlantic states.
Teets and her Virginia colleagues will survey the same sites that were sampled during previous studies prior to the arrival of white-nose syndrome and evaluate whether bat communities have changed since the previous survey.
“We want to understand what habitats need to be conserved and the effect white-nose syndrome is having on individual bat species populations and their habitat use, so it’s very important to understand how population numbers and community structure are being affected by white-nose syndrome and other stressors,” Teets said.
An April 2011 article in Science presented analysis estimating the value of bats to North American agriculture industry is roughly $22.9 billion per year. The estimates include the reduced costs of pesticide applications that are not needed to suppress the insects consumed by bats.
First-ever South Carolina statewide bat population study
The North American Bat Monitoring Program (NABat) is a nationally coordinated effort to collect bat population data that can provide wildlife managers with the information they need to effectively manage bat populations, detect early warning signs of population declines and estimate extinction risk
NABat was developed by USDA Forest Service research ecologist Susan Loeb and colleagues from the U.S. Fish and Wildlife Service, U.S. Geological Survey, National Park Service, Canadian Wildlife Service, Bat Conservation International, and National Institute of Mathematical and Biological Synthesis.
As part of the NABat project, Clemson wildlife ecology student Ben Neece is leading the first-ever South Carolina statewide bat survey.
Neece uses both mobile and stationary surveys to collect bat echolocation sounds from 38 survey cells, or map quadrants, across South Carolina. The survey sites are chosen for an array of factors, including habitat variety, maximum bat species diversity and low clutter that would interfere with recording.
It’s a big job, and Neece is relying on assistance from government agencies such as the South Carolina Department of Natural Resources, USDA Forest Service, Department of Energy and South Carolina Forestry Commission, but the survey also relies on help from South Carolina Master Naturalists, who have undergone training through Clemson University Master Naturalist Program and the Edisto Island Open Land Trust.
Last summer, his first of the survey, Neece collected approximately 60,000 sound files. After using computer software and noise filtering technology to cull insect sounds and other ambient noise, he was left with 27,000 bat calls. He then used automated classification software to help identify and categorize the bat calls by species.
“Many bat calls are similar,” Neece said. “But there are subtle differences by species. Since the bat calls are at frequencies humans can’t hear, the computer software helps us identify them visually. The ones that are too similar for the computer software to distinguish, I categorize myself.”
South Carolina is home to 13 bat species, including the big brown bat (Eptesicus fuscus), Mexican free-tailed bat (Tadarida brasiliensis), tri-colored bat (Perimyotis subflavus), Eastern red bat (Lasiurus borealis), Eastern small-footed bat (Myotis leibii), evening bat (Nycticeius humeralis), hoary bat (Lasiurus cinereus), little brown bat (Myotis lucifugus), Northern long-eared bat (Myotis septentrionalis), Northern yellow bat (Lasiurus intermedius), Rafinesque’s big-eared bat (Corynorhinus rafinesquii), Seminole bat (Lasiurus seminolus), silver-haired bat (Lasionycteris noctivagans) and Southeastern bat (Myotis austroriparius).
Neece will finish his project in the spring of 2017. Then he will turn over his data to the NABat program and the South Carolina Department of Natural Resources, where it will serve as the foundation of future efforts to stem the catastrophic loss of bat life.
Did you know? Bats and tequila
Long-nosed bats, which inhabit the dry portions of the North American tropics from El Salvador to northern Mexico, are the primary pollinators of the agave plant, from which tequila is derived. It’s believed the the association between long-nosed bats and agave is so strong that the demise of long-nosed bats would threaten the survival of the agave plant and the tequila industry.