For the first time, scientists are observing signs that certain bat colonies are stabilizing after being ravaged with white-nose syndrome, a disease that has killed millions of bats throughout the United States in less than a decade. In addition, new research is shedding light on how the disease works, bringing researchers one step closer to finding a way to stop it from wiping out entire colonies of bats.
“It’s encouraging — the one glimmer of hope we’ve been able to find through all this,” said Christina Kocer, Northeast White-Nose Syndrome Coordinator for the U.S. Fish and Wildlife Service.
White-nose syndrome was first discovered in the U.S. in 2006 in a cave in New York, and since then has spread rapidly, killing more than 5.7 million bats and approximately 80 percent of the bat population in the northeastern US.
Named for the white fungus that appears on the muzzle of infected bats, white-nose syndrome kills bats as they hibernate during the winter. Scientists believe the disease was transported to the U.S. unknowingly by spelunkers, people recreationally exploring cave systems in Europe, where bats appear to have developed resilience to the fungus.
“It’s traveled very quickly,” said Kocer. “Twenty-five states and five Canadian provinces now have this disease.”
Of the 47 bat species living in the U.S., seven cave-hibernating species have been confirmed to have white-nose syndrome.
Maine appeared to be insulated from the disease until spring 2011, when biologists found white fungus growing on bats in two caves in Oxford County. Since then, three bat species in Maine — little brown bats, northern long-eared bats and eastern small-footed bats — have seen somewhere between 80 and 100 percent declines in their populations due to white-nose syndrome, according to a previous BDN story.
The “glimmer of hope” comes from Aeolus Cave in Vermont, where biologists recently found little brown bats surviving despite years of exposure to the disease.
“It’s important to note that only in this one species — the little brown bat — have we been able to find this,” Kocer added. “The next question is, why are they surviving? What’s different about them? We’re still working on that.”
Little brown bats were once the most abundant bat species in the U.S. But when white-nose syndrome began to spread, they were one of the hardest hit. Just a few years ago, scientists predicted that if the little brown bat population continued to decline at the same rate, they would be extirpated from the U.S. within 15 years.
In Aeolus Cave, once home to 250,000-300,000 bats each winter, the disease killed about 90 percent of the hibernating bats, the majority of which were little brown bats.
“That’s still 25,000 to 30,000 [hibernating in the cave], which seems like a lot, but it’s a lot fewer than there used to be,” said Alyssa Bennett, wildlife specialist of the Vermont Fish and Wildlife Department.
Bennett is a part of a team of scientists researching Aeolus Cave bats by capturing them before hibernation and attaching tags to their forearms and backs. Over the past two years, the team has found that the survival rate of little brown bats has drastically increased. More than 50 percent of tagged little brown bats are surviving the winter, in comparison to the previous survival rate of about 10 percent.
“It appears we’re seeing bats stabilize at this really low level,” Bennett said. “But the idea that we could see a lot of bats again in our lifetime is just not a possibility. They don’t reproduce fast enough.”
Each summer, Bennett and other Vermont wildlife biologists observe female little brown bats gather into nursery colonies, where each female bat gives birth to one pup.
“We hear sometimes in the news that the population is bouncing back or recovering, but I would say we don’t really have evidence of that,” Bennett said. “What we’re seeing is some stabilization, and that’s very exciting.”
The Vermont study is just one of several studies taking place across the country in an effort to understand and manage white-nose syndrome.
In 2009, the U.S. Fish and Wildlife Service led a team of federal and state agencies and tribes in preparing a national white-nose syndrome management plan to address the threat to hibernating bats. The plan is a framework for coordinating and managing the national investigation and response to the disease.
As a part of that effort, researchers transported 30 infected bats to northern Maine in December 2012, placing them in old bunkers at the former Loring Airport Base, now the Aroostook National Wildlife Refuge. The experiment was to study whether artificial, sterilized hibernacula could be used to increase survival rates of bats infected with the disease. Just nine of the 30 bats survived the winter.
More recently, a Wisconsin study was published in December that sheds light on exactly how white-nose syndrome kills bats.
The study, funded by the U.S. Geological Survey, is based on a three-month experiment in which scientists used the doubly labeled water method and clinical chemistry to evaluate energy use, body composition changes and blood chemistry in 60 hibernating little brown bats in a lab setting.
“We need to understand why bats are dying from this infection in order to identify what types of treatments and solutions will be effective,” said the study’s lead author, Michelle Verant, wildlife veterinarian at the University of Wisconsin-Madison.
In the study, it was discovered that infected bats burn twice as much energy as healthy bats during hibernation, which ultimately results in starvation. This explains why scientists have observed infected bats fly outside the cave in the depth of winter in search of food.
“One of the key roles bats play in our ecosystem is insect control,” Verant said. “They’re voracious insect predators. One little brown bat, which would fit in the palm of your hand, can consume up to 1,000 insects in an hour in the summer. Multiply that by millions of bats.”
Verant is now working on another bat project, studying how environmental conditions within caves and mines can affect the severity of white-nose syndrome.
“We’ve had some promising observations in the field supporting that bat populations with white-nose syndrome are surviving at certain sites, and we think its due to the temperature and humidity in those sites,” Verant said. “We’re working at different sites across the country to measure environmental conditions and understand how these sites are supporting bats.”
Studies of natural bacteria and skin chemistry of bats have led to new lines of research for treatments using biological or nonchemical agents for bats at risk of infection. Scientists are also working to develop vaccines to boost bats’ resistance to the disease.
“There’s some really cool research coming out,” Kocer said. “A lot of research is going into treatments, and the preliminary stuff looks pretty interesting in the lab, but there’s still a long ways to go until we can actually apply it and put it on bats.”
For information about white-nose syndrome, visit whitenosesyndrome.org.