One of the worst wildlife die-offs in recorded history is unfolding in caves and mines throughout the north- and southeast. A disease dubbed white-nose syndrome is killing off bats at a mortality rate that, at some sites, approaches 100 percent. Bats infected with the fungus thought to cause the disease awake early from hibernation, or don’t slumber as deeply as they should, and burn through their fat reserves too fast. They emerge from their caves before winter has ended and then starve for want of insects. To save energy, bats shut down their immune systems during hibernation, which makes them even more vulnerable to the illness in winter. (For more on the specific mechanisms of how the fungus may sicken and kill bats, see my previous post, “Warming caves, a stop-gap measure to thwart WNS?”)
I first wrote about white-nose syndrome at the Science in the Triangle blog (Hibernation Devastation) after attending a lecture about the status of the disease in December 2009. (That post was later reprinted in The Naturalist, a publication of the N.C. Museum of Natural Sciences.) Tomorrow, 9/6, my second published story on white-nose syndrome will run in the Charlotte Observer’s Sci-Tech section, as well as in its sister paper, the Raleigh News & Observer. But you can find it online, tonight, here. As always, there is never enough space in the print edition to include all the cool things gathered, and reported on, when writing the story. So I’m making this blog post a grab-bag of the parts that got cut or that I researched but did not have space to include.
The predicted path:
One of the most fascinating aspects of the spread of this disease, in my opinion, was a set of predictive maps published in Jan. 2009 by Bat Conservation International showing the path of the disease moving southwest along the Appalachian mountains. They illustrated the migratory path of bats and their hibernacula as a gray cloud spreading down the spine of the ancient mountain chain, and they overlaid a series of yellow arrows over the gray cloud, depicting where the disease would travel as it spread between hibernacula. They also documented counties known to be infected with the disease (or suspected to be) in red. An early rendition of the maps showed the disease shooting right past North Carolina, despite the western part of the state being covered in swaths of gray (indicating the presence of hibernacula). Here is a picture of their map, updated as of 7/7/2010:
Despite ricocheting 450-miles south and west this winter and shooting from southern Virginia to far western Oklahoma, white-nose syndrome sped past North Carolina. Why, I wondered, would NC be exempt from this disease? So I called BCI and asked. As early as January 2009, Bat Conservation International predicted a path moving southwest along the spine of the Appalachian mountains based on data gathered from radio telemetry and banding observations, which gave scientists clues to how bats migrate and move around the landscape. Their published maps showed the disease speeding next to, but not within, my state. “It’s eerie how the maps have come true,” said BCI conservation biologist Mylea Bayless. “But the reason we didn’t show it traveling into North Carolina is not because the state is immune, it’s just a fluke, a paucity of data.” The scientists at BCI did not have enough information, so they simply did not show a route. In an uncanny coincidence, that is also how events have played out — so far.
On the severity of this disease:
In May of 2009, a group of leading U.S. scientists from 12 states and federal wildlife agencies warned in a consensus statement that the disease “has caused the most precipitous decline of North American wildlife in recorded history.” Their statement also estimated bat deaths to have exceeded 1 million at that point in time, and while no one has an updated estimate, it’s safe to assume the numbers swelled further in the 2009-2010 winter.
On the evolution of the fungus, Geomyces destructans, thought to cause the disease:
Bats in Europe may have been affected by this fungus in their evolutionary past, says Mylea Bayless, a biologist with Bat Conservation International. The fungus, at first thought to not occur at all in Europe, has now been found in the Old World too — though bats there are unharmed by it. This suggests they may have co-evolved with it, Bayless says. So far, there is no evidence that bats in the New World have any resistance to the disease. Bayless notes that bats in Europe tend to be more thinly distributed, and that they do not gather in hibernacula as large as the ones that form in the New World. She speculated that this may be an after-effect of bats in the Old World having co-evolved with the deadly fungus.
More on the fungus:
The fungus thought to cause the symptoms of white-nose syndrome is a cold- and humid-loving organism that grows best between 41 and 57 degrees Fahrenheit. It burrows into the bat’s skin, covering their nose and muzzle, ears and wings in white fungi. It’s thought that the discomfort of the infection causes the bats to awake from hibernation, which speeds their metabolism and causes them to burn through their fat reserves before winter is over. Bats in harsher climates farther north that hibernate for longer periods of time are thought to be harder hit by the disease than bats that live in milder southern climes and that hibernate for shorter periods of time, or that do not go into deep hibernation. While scientists were at first hesitant to say the fungus caused the disease, the evidence is circling tighter around it. “We think the fungus is clearly the smoking gun,” Bayless says. “We know that the fungus is perfectly capable of causing the disease, but lab tests are not completed that replicate the disease process.”
On closing caves in North Carolina:
In May of this year, The Nature Conservancy altered the path of their guided hikes to Bat Cave Preserve and Rumbling Bald just east of Asheville, leading guests to within 150 feet of the one-and-a quarter-mile-long cave system instead of into the cavern entrance as they did in the past. The move reflects a trend of conscientious landowners and regulators closing down human access to caves because people may play a role in moving the disease between caves. Bat Cave Preserve attracts about 250 tourists each year. “Our take on it is that we know this syndrome is affecting the bat community, and we want to be as conservative as possible, while being proactive in protecting the bat populations there,” says Cat Burns, science director of the N.C. chapter of the conservancy. “We don’t know that it is spread by humans, but we also don’t know that it is not.” Past surveys have shown that caves on the conservancy property may hold 250 to 300 bats from four or five species on and off throughout the year, Burns said. Bats using the cave regularly include the eastern pipistrelle, big brown bat, little brown bat, northern long-eared bat and eastern small-footed bat. The last two are state-listed as species of special concern. A federally-endangered Indiana bat was sighted in a cave in Rumbling Bald last winter, this species is thought to be an occasional though uncommon visitor to the area.