By Jeff Nations
The worst may be over for Virginia's native cave-dwelling bat population, but the damage to the state's night-time fliers has been nothing short of catastrophic.
The emergence of a deadly disease, White-nose syndrome (WNS), just a few years ago has rapidly ravaged large numbers of cave-dwelling bats in Virginia and throughout the eastern United States. The disease, first detected in New York state in 2007, has quickly spread as far west as Missouri and Wisconsin and has ravaged hibernating bats wherever it has been found. So far, the fungal disease, named for the white fungus Geomyces destructans, has been confirmed in 20 states.
"Every cave in Virginia, really, is a White-nose cave," said Wil Orndorff, the Karst Protection Coordinator for the Virginia Department of Conservation and Recreation. "The disease has spread so much. We haven't seen a negative cave in Virginia in the last year. The disease is an epidemic. The initial wave killed huge numbers of animals."
Among the hardest hit are two bat species which not long ago made up the vast majority of Virginia's hibernating bats -- the Little brown bat and the Eastern pipistrelle, or Tri-colored bat. Orndorff said that before the onset of WNS, those two species combined to represent 99 percent of Virginia's hibernating bat population. But since the peak of the WNS epidemic in the last three years, the mortality rate for those two species has been estimated at 90 to 95 percent in Virginia. WNS was first detected in Virginia in Feb. 2009.
"This is the most rapid decline of a population that anyone has ever seen," Orndorff said. "It's kind of like the Bubonic plague for bats, only the mortality rate is much higher. This is much more widespread."
The numbers are sobering, but Orndorff said about half of Virginia's bat population isn't affected by WNS at all. That segment, tree bats which migrate to the state during the summer months before heading south as far as Mexico and Central America for the winter, are much less likely to come into contact with the disease. The cold-loving fungus, infects the skin of the muzzle, ears and wings of hibernating bats. The resulting skin irritation impacts the affected bats' hibernation, prompting untimely emergence during the winter months. Forced to consume stored fat reserves, the bats become emaciated and can die of starvation.
Orndorff said that of the eight native hibernating bat species in Virginia, seven have been affected by WNS. The mortality numbers are based on sampling and not on full-scale population counts, but the evidence of a widespread die-off is strong. Orndorff said that in Bland County, which once had the state's highest concentration of Little brown bats in one location, a population of 16,000 has dwindled to less than 200. In Tazewell, the population of Little brown bats dropped from 6,000 to fewer than 30 in just two years.
"Little brown bats were really growing in numbers," Orndorff said. "The state's population of Little brown bats 10 years ago was probably higher than in the time of Christopher Columbus. Little brown bats roosting in buildings, mines, quarries -- they're really great adapters. But when you reach a certain population density in species, they become very susceptible to an epidemic. Something was bound to happen."
With few survivors left among that initial population of Little brown bats and Tri-colored bats, the epidemic has begun to subside. Orndorff said those bats that still remain still show signs of the disease, but have not died off at the rate previously seen. That's encouraging, but Orndorff said WNS is likely a continuing threat since the spores of the fungus can survive for years without a host.
"That remains to be seen," Orndorff said. "We're still seeing survivors harboring the fungus."
Just where the disease originated remains a mystery, as well, although it bears strong similarities to a similar fungal infection which affects European bats. The disease is generally not fatal there. From that initial outbreak in New York, the disease has rapidly spread. Orndorff said that while it is a good idea for cavers to be mindful of the potential of spreading the disease and take necessary precautions by decontaminating clothes and equipment, there has been no evidence showing humans have helped spread the disease which is transmitted from bat to bat.
Orndorff said there is hope that other species which are largely or totally unaffected by WNS will move in to fill the void left by the disappearance of so many bats. The Virginia big-eared bat, for example, has proven completely resistant to the WNS outbreak. Its population is limited, however, and the bat tends to prefer higher elevations.
"The species we're really keeping an eye on is the Gray bat," Orndorff said. "They still get [WNS], but they don't die from it. They may come into the area in the next 20 to 30 years. They're the same genus, and they have the potential to expand their range."
If and until that happens, the night skies throughout the eastern U.S. will likely host significantly less bats. That impacts insect control and crop pollination.
"There's been a lot of good science and a lot of good work done on it," Orndorff said. "We've been kind of behind the eight-ball, but there's good work being done right now."
Contact Sports Editor Jeff Nations at 540-465-5137 ext. 161, or firstname.lastname@example.org>