MARLBORO — Bats are dropping like flies.
With three-quarters of the bat population dead, scientists fear some species, such as Vermont's Little Brown Bat, could be headed for extinction.
Hibernating bats are succumbing to a condition called White Nose Syndrome (WNS) caused by a newly introduced cold-loving fungus. The fungus looks like a gentle dusting of snow. In reality, it burrows deep into the bats' skin, according to Scott Darling, a wildlife biologist with the state's Agency of Natural Resources.
More than a million hibernating bats have died from WNS since 2006.
Symptoms of WNS include weight loss and flying during winter in daylight.
“They're sitting ducks. They're uniquely vulnerable to diseases [during hibernation],” said Jeremy Coleman, the national White Nose Syndrome coordinator for the U.S. Fish and Wildlife Service.
Darling estimates Vermont has lost 75 percent of its bat population - or about 500,000 bats - so far, including about 50 percent of the endangered Indiana Bat population. If the rate of death continues, Vermont's common Little Brown Bat will be extinct within 16 years.
Coleman said scientists are still trying to “define the disease” and will need to better understand how the fungus spreads and kills before they will have effective means to combat it.
At this early stage, scientists believe WNS spreads through bat-to-bat contact and environmental contact. They are still unsure if it spreads during warm weather.
What scientists do know, said Darling and Coleman, is that hibernating bat colonies infected with the fungus Geomyces destructans show a 90-to-100-percent mortality rate.
Coleman said bats' own hibernation may fuel their susceptibility to the fungus's destruction.
According to Coleman, bats enter a state of torpor during hibernation, mid-April to November, where their heartbeats drop from one or two beats per minute and their metabolic processes slow. Their body temperatures drop to match the ambient winter temperature of the caves or mines where many bats choose to hibernate.
Their immune response also slows during torpor, allowing the fungus undisputed access to the bats' bodies.
'From fear to fascinating'
It's challenging to convince people of bats' importance because so many are afraid of them, Darling told an audience last month as part of an ongoing lecture series at the Southern Vermont Natural History Museum in Marlboro.
Vermont has nine species of bats. The most common state bat in 2007, the Little Brown Bat, weights 7 grams or roughly three pennies. It will also enter houses as will the Big Brown Bat, the only bat to winter over in attics.
The Tri-Colored Bat, Northern Long-Eared Bat and endangered Indiana Bat prefer dense woods and dead trees. The Small-Footed Bat, having the dubious honor of being on the state's threatened list, likes roosting in south- and west-facing cliffs.
Three bats migrate from Vermont to points south: the Red Bat, Hoary Bat, and Silver-Haired Bat.
The Silver-Haired, said Darling, was once considered common but has only one recorded sighting in the past 10 years.
The Hoary Bat, Vermont's largest at 25 grams, migrates as far as the Caribbean and Mexico.
Bats evolved from lemurs 53 million years ago. The bones in their wings are hand bones. They live about 20 to 30 years, and females give birth to about one pup per year.
Empty caves
According to the U.S. Fish & Wildlife Service's website, the first suspected cases of WNS showed up in a 2006 photograph of hibernating bats covered in a white substance snapped by a caver in the Howe Cave in Howe, N.Y.
The following winter, bats with white noses, bats leaving the hibernation colonies in the middle of winter, and “a few hundred dead bats in several caves” caught the attention of the New York Department of Environmental Conservation, which documented the first cases in January 2007.
By 2008, biologists had confirmed WNS sites in Vermont, New Hampshire, New York, Massachusetts, and other states as far south as Virginia. This year, new confirmed sites have cropped up in Ontario and Québec in Canada, as well as northern New Hampshire and Tennessee. Suspected sites can be found as far west as Oklahoma.
According to a map on the Fish & Wildlife Service's website, the fungus in Vermont was first confirmed in Bennington, Rutland and Orange counties in 2007–08, then spread to Windham and Windsor counties in 2008-09.
Coleman said few bats die the first year the fungus is discovered in a cave or mine.
“Mass death” tends to occur within the second and third years.
Many healthy bats, he said, eventually abandoned many of their long-time hibernation locations like Aeolus Cave in Manchester, once the hibernation home of 300,000 bats.
On the move
Darling and Coleman said scientists are watching the fungus as it moves south into warmer climates as the bats' migrate.
“As it's moving, we don't know what to expect. We're hoping we won't see the same reaction,” Coleman said.
Scientists still don't know if the fungus infects bats in the summer. Also, bats experience a shorter hibernation period in warmer climates that could give the fungus less time to take hold and more time for the bats' immune systems to fight.
Despite some earlier, but limited, success with an insecticide, a cure for WNS is still out of reach, said Darling and Coleman.
According to Coleman, fungi can prove tough to kill and the available insecticides require multiple applications.
Darling said handling bats in their delicate torpor state during past applications may have killed just as many as it saved.
The other issue with insecticides is their potential to harm the natural and unique ecosystems within caves that have evolved over millions of years.
Coleman feels the ideal solution would be to find a “biological control agent” like an enzyme or bacterium naturally occurring in the bats.
The best option right now at the feds' disposal, said Coleman, is controlling the fungus's spread.
But, he adds, humans can't control the movements of bats. The Fish & Wildlife Service is asking people modify their behavior and stay out of caves and mines and thoroughly decontaminate any gear or equipment.
These warnings hold true for recreational cavers and scientists alike, said Coleman. The National Wildlife Refuge System has already closed a number of caves to try and slow the spread.
He adds this request has met with resistance from people feeling the government is dictating whether people get to explore caves or mines - or not.
“If we can prevent [the spread], even for a year or two, we can gain time,” said Coleman.
Origins of a fungus?
Although research is in the early stages, it seems North American bats can look to their cousins in Europe for the fungus's source, said Darling.
The current hypothesis, according to Coleman, is that the fungus has been present in Europe in one form for 30 years without the mass deaths.
Coleman also said scientists think the fungus was introduced to the Northeast through Howe Caverns, a 10-million-year-old show cave just west of Albany, N.Y., that's open to visitors year-round.
Howe Caverns connect to Howe Caves, where the fungus was first spotted.
“The best scientific information we have suggests people are spreading this [as much as the bats are],” he said.
Easier protecting pandas
A decline in bat population may be music to the ears to the tennis-racket-and-broom-welding members of society to whom bats are known as “dirty rats with wings.” But, said Darling and Coleman, consider their place in the ecosystem.
Bats are the primary predator of nighttime flying insects like moths and mosquitoes. A single bat consumes half or sometimes up to its full body weight every night.
In human terms, said Darling, that's about 175 quarter-pound hamburgers.
Coleman said the service doesn't know the long-term ecological impact if bats become extinct but the potential exists for populations of tent caterpillars, disease-carrying mosquitoes and agricultural pests like corn moths to run unchecked.
“Bats do have value,” said Coleman.
Coleman finds interesting the academics of tracking the fungus and learning about bats' responses.
“The reality is horrifying,” he said.
Darling said the Agency of Natural Resources continues to monitor bat populations, provide outreach opportunities for people to learn more, and work with landowners with hibernation colonies.
On Oct. 6, the U.S. Fish & Wildlife Service announced six grant awards totaling $1.6 million for research into the cause of WNS in bats and to identify ways to manage it. The Preventing Extinction program and a congressional appropriation for WNS work provided the funding.