Bat Die-Off From White Nose Syndrome Shows A Decline

Mar 13, 2014

A crisis in the form of a mysterious disease called white nose syndrome threatening Vermont’s bat population may be stabilizing. 

The alarming number of bats killed by this disease in recent years prompted the state to list three of Vermont’s nine species as endangered, but now perhaps, some good news that the rate of the decline may be slowing, even as scientists race against time to find a way to reverse the trend of bat die-off.  

Scott Darling is the bat project leader for the Vermont Department of Fish and Wildlife, and has been tracking these developments very closely. 

When the disease first hit Vermont in 2008 and 2009 mortality rates reached 90 percent in populations of cave bat species, like the little brown bat and the northern long-eared bat.

“So those are just tremendous precipitous declines in just a two to three year period. But now there are some observations that the percent of the population that is dying from white nose syndrome each year is declining dramatically from those very high figures,” Darling explained.

"There are some observations that the percent of the population that is dying from white nose syndrome each year is declining dramatically from [the 90 percent mortality rate]." - Scott Darling, Vermont Department of Fish and Wildlife

Scientists don’t know what white nose syndrome is, or what’s causing it, and they don’t know what is slowing this decline in the morality rate.  

“We do have observations that we have bats that have been surviving multiple years and our research cites that 50 percent of the bats that had been banded in the pervious year showed up again in the hibernacula, in the cave. And we know there are fewer observations of dead bats on the landscape during the wintertime, which was the primary source or mortality when the disease first hit,” Darling said.

The sick bats were coming out of caves in winter because they were becoming dehydrated and emaciated. Scientists can only speculate that the bats left the caves because they knew they were going to die if they stayed.

“Those that left the cave in January and February, of course, encountered below freezing temperatures,” he said. “Bats simply can’t survive in those situations.”

This past winter, the Vermont Fish and Wildlife Department and the New York Department of Environmental Conservation have worked together on a project to glue little radio tags on the backs of 450 little brown bats at a major cave in Vermont.

"We know there are fewer observations of dead bats on the landscape during the wintertime, which was the primary source or mortality when the disease first hit."

“If a proportion of those bats come out before they normally would, we would consider those bats that would not survive. But if we do observe bats coming at a normal emergence period, which is mid-April, that will give us a real good estimate on the proportion of bats that are surviving the winter here at this cave,” Darling explained.

In another experiment, scientists transported 40 bats from Vermont and 40 from New York to an artificial cave, an abandoned military bunker in Maine. Darling refers to this as a "Noah’s Ark" alternative, designed to buy time to keep the bats alive to find a treatment. But what they found is that if you take infected bats and move them to a clean environment, like the bunker, they will still die from white nose syndrome. Scientists are now focusing on trying to get the best estimate of survivorship in an affected cave.

Vermonters can help the bat population by letting bats get out of their houses if they get in. They can also put up bat houses, and they can always call the Vermont Department of Fish and Wildlife for assistance when dealing with bat populations in the neighborhood.