New estimates calculate that between 5.7 million and 6.7 million bats have died because of a White Nose Syndrome epidemic in the eastern United States and Canada.
The figure replaces a previous assumption that at least 1 million bats had been killed by the fungal infection. But the new number, and how it was reached, has ratcheted up the debate over how best to protect the flying insectivores.
“Although it’s a really big increase, it wasn’t a surprise to us,” said Ann Froschauer, White Nose Syndrome communications leader with the U.S. Fish and Wildlife Service. “The 1 million number was stated in 2009, and we hadn’t really updated that number for the last three hibernation seasons. We’ve had several years of significant disease spread. So that’s the estimated number of bats killed since winter 2006 to present, not including this winter.”
What that number means is less clear. It was part of congressional testimony that helped justify $4 million for White Nose Syndrome research in the 2012 federal budget. But it hasn’t narrowed the gap between wildlife advocates and cave explorers on the policy question of closing caves to the public.
“I’ve been pushing for well over a year to update that number,” said Peter Youngbaer of the National Speleological Society, which has closely monitored the fungus outbreak. “But 6.5 million bats is the top end of the estimate of the entire population of little brown bats in the entire United States. The best I could figure out is they’re using an assumption that virtually all the little brown (bats) have been wiped out, which we know isn’t true. I know a colony in New York where there are still thousands of them. I think that number is high.”
Mollie Matteson, a conservation advocate for the Center for Biological Diversity, countered that the figure shows continued effort is needed to stop the spread of the disease.
“It is really premature to say little brown bats are hanging on” Matteson said. “Some appear to be surviving , and that’s definitely good news, but the populations have been whacked down to an incredibly small fraction of what they were. I think we could hardly say they’re doing OK now.”
The Center for Biological Diversity has led a national effort to get federal land managers to close access to caves on public lands and work harder on finding a response to the disease. Matteson said that effort was continuing, along with Freedom of Information Act requests to learn what policy changes those agencies were considering.
Froschauer said the agency used two methods to build its new estimate. One used a mathematical formula where the known population estimates and declines of bats in some states was extrapolated across all the states and Canadian provinces where the disease has been detected.
The other gathered estimates from state wildlife officials of known declines and added them together. Froschauer said both methods produced significantly similar results.
But Youngbaer said that number doesn’t give any indication if the disease spread is getting worse or better.
“The story, and the reaction to it, will drive public policy and management decisions like where money is invested,” he said. “It needs to be driven by harder numbers than what they’ve given us. It’s a scary number. It can make folks take actions they might not otherwise.”
That’s particularly important in the western United States, where White Nose Syndrome has not yet been reported and many people like to explore caves. Montana has caves that are among the deepest in North America, and Lewis and Clark Caverns is a popular state park.
It also has 15 species of bats, but little research on their populations or habitats.
“We don’t even know where our bats hibernate,” said non-game wildlife biologist Kristy Dubois of the Montana Department of Fish, Wildlife and Parks. “They have large hibernating colonies back East, but the largest one we have is just over 1,000 in one hibernacula in Montana. The rest are a dozen bats here or handful there. We think a lot of our bats may hibernate in crevices rather than caves, and some may migrate out of the state.”
To help answer some of those questions, FWP has been gathering volunteers to place acoustic monitors and data loggers at known or suspected bat territories.
“We know a lot of bats come out in the middle of winter, when there’s still snow on ground,” Dubois said. “Especially big brown bats come out to get a drink , and some rivers have insect hatches year-round that they feed on. But we don’t have any way to quantify that. We’re just trying to get some baseline data.”
Similar efforts are occurring around the country, Froschauer said, with new data expected around April. Meanwhile, the congressional money will fund a three-pronged research plan. The goal is to determine how the fungus is transferred and which bats are most susceptible; to confirm how fast the disease develops once it arrives in a new area; and to identify non-chemical options for protecting wild bat populations.
“When I went to my first affected site and saw the devastation firsthand, it took seeing the carnage to grasp the big picture of what it actually means,” Froschauer said. “There used to be 100,000 bats in there and now there are five. I don’t think there’s a lot of hope from the scientific community that it won’t spread west. Hopefully you guys get to keep it at bay a while.”