Hying himself to the bat cave may be good for Batman, but it’s increasingly dangerous for cave-dwelling bats, thanks to a mysterious disease.
This story starts in a cave in upstate New York in 2006. A caver exploring it noticed some bats there, including dead ones, had a white substance on their muzzles. Scientists at state and federal agencies began looking into the issue and found that a fungus, Geomyces destructans, was infecting the skin of the muzzle, ears and wings of bats in colonies that hibernate in caves. The condition was dubbed White-nose Syndrome (WNS).
Colonies of cave-dwelling bats began to decline precipitously from WNS. The U.S. Fish and Wildlife Service’s website characterizes the disease as “devastating” and reports that it’s been spreading south and west “at an alarming rate,” killing more than 5.5 million hibernating bats and making WNS “the worst wildlife health crisis in memory.”
By the end of the 2011-2012 hibernating season, occurrences had been confirmed in 19 states and four Canadian provinces, according to a website (whitenosesyndrome.org) set up by USFWS and partnering organizations to disseminate data on the disease. In June, Iowa became the 20th state when its Department of Natural Resources reported low levels of the fungus had been discovered on bats in a cave there. North America appears to be the epicenter of WNS at this point, although the fungus has been found on a few bats in Europe and there are growing concerns about the disease there.
The exact cause of the deaths remains unknown, says USFWS, but infected bats have been observed displaying abnormal behaviors in their cave hibernacula (hibernation sites), such as movement toward the mouths of caves and daytime flights during winter. This may cause them to use up their stored fat reserves quicker and become emaciated, a characteristic documented in bats that die from WNS.
Virginia is now assisting the U.S. Geological Service’s National Wildlife Health Center with a study on the persistence of WNS fungal spores in caves and mines in the eastern United States, says Virginia Department of Game and Inland Fisheries (VDGIF) wildlife biologist Rick Reynolds, who has been monitoring bat populations in the mountain regions “for quite some time.” Virginia has eight cave-dwelling bat species, which are found mostly in the state’s mountain regions. Three of these – gray bat, Indiana bat and Virginia big-eared bat (the state bat of Virginia) – are federally listed as endangered.
Data VDGIF collected over the winter indicated that WNS had spread in Virginia’s primary cave areas. Only Lee County, at the tip of the panhandle, had no documented occurrence – yet.
Two of Virginia’s most common cave-hibernating bat species have had the steepest documented decline from the disease, says Reynolds. The little brown bat fell from a combined high of slightly more than 5,000 individuals in 2009 to just 125 individuals in 2012, a decline of more than 95 percent in four years, and the tri-colored bat (formerly known as eastern pipistrelle) showed a similar decline.
Some bat species, known as tree dwellers, may overwinter in tree cavities and buildings, says Reynolds, but most species that are not cave dwellers tend to migrate south instead, escaping the disease.
It’s the cool temperature in the caves that makes the WNS fungus thrive. Reynolds says that, since the fungus disappears at temperatures above 70 degrees, data on it has to be collected in the winter. Researchers have to swab the noses of bats that aren’t white to ensure they haven’t been infected, since the fungus may not be apparent in its early stages. To avoid further disturbing colonies that are already at risk, data collection was reduced this past winter.
With bats living a relatively long time and having only one pup (offspring) a year, it’s questionable whether colonies infected with WNS can recover, Reynolds and other bat experts say.
So why should we care? Aren’t bats just nocturnal rodents that carry rabies and get tangled in our hair?
Myths have abounded about bats since before written history, and Bram Stoker’s associating them with vampires in his novel “Dracula” didn’t help.
Counter to the myths, bats are not rodents. “Most scientists agree that bats are far more closely related to primates,” wrote Merlin D. Tuttle, the founder and science director of Bat Conservation International, in his book “America’s Neighborhood Bats.” It is true that bats can carry rabies, but they are not as likely to as foxes, skunks and feral cats.
Bats’ erratic flight at dusk can be startling, but they’re aiming at flying insects, not our hair. Except for a few nectar-eating species along the Southwestern border, all U.S. bats are insectivores. Bats fly at night, which makes collecting data on their feeding habits problematic, they are generally considered an important control for insect populations.
Tuttle points to individual mouse-eared bats, “the most widely distributed of bat species,” which “can catch up to 600 mosquitoes in an hour” and to the 20 million free-tailed bats from Bracken Cave colony in Texas that, he says, “eat a quarter of a million pounds or more of insects in a single night!”
By controlling insect populations, bats help control the transmission of disease by insects and diminish crop destruction and the associated use of pesticides. USFWS director Dan Ashe, in an April press release, said simply, “Bats are crucial to our nation’s ecosystems and our economy.”
USFWS is now offering $1.4 million in grants to states to help address the spread of WNS, the resultant loss of cave bat populations and the threat to federally listed bat species.