Heather Kaarakka
Paul White, a DNR biologist, tests hibernating little brown bats for the deadly white-nose syndrome.
White-nose syndrome, the fungal disease decimating bat populations in the eastern United States, continues to spread in Wisconsin and is starting to reduce the flying mammals’ numbers, according to a recent survey by the state Department of Natural Resources.
Over the winter, research scientists inspected and tested bats in the caves and mines where they hibernate. They found evidence of the disease in 42 out of 74 sites, including in six new counties, according to a DNR newsletter.
Bat numbers are down, particularly where the disease is well established. At the mine in Grant County where the fungus was first discovered in the state, the bat population has declined 94% in the past two years.
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Like other hibernating animals, bats rely on fat stores to get through the winter. Usually they rouse and move around the cave every 15 to 20 days during hibernation, says Paul White, DNR conservation biologist. Infected bats wake much more frequently, as often as every three to five days, so they burn through their energy stores more quickly, putting them at risk of starvation.
For this reason, white-nose syndrome is generally only fatal to hibernating species, including the little brown bat, the state’s most common. Bats that migrate in the winter generally don’t succumb to the illness.
This understanding of the disease came out of Michelle Verant’s research at the USGS National Wildlife Health Center, on Madison’s west side. The center, along with a number of labs at the UW, puts Madison at the forefront of white-nose syndrome research and methods to treat it.
One strategy currently being tested is a vaccine. If the vaccine could slow the growth of the fungus enough for the bats to get through hibernation in relatively good health it could improve their survival rate, says Tonie Rocke, a research scientist with the National Wildlife Health Center.
When hibernating bats occasionally wake they groom themselves and each other, licking water vapor off of their fur. When they do this they could ingest a vaccine applied to their coats.
In the vaccine, Rocke and her colleagues are using a viral vector shown to work in a rabies vaccine for bats, which they are also developing. The lab trial currently underway is testing whether they have found an antigen that can effectively fight the WNS fungus. If the trial is successful they may be able to test the vaccine at an actual hibernation site next winter, Rocke says.
Another approach being studied is a bacterial treatment. Last winter, the DNR participated in a trial at a mine in Wisconsin. The results are not yet in, but even if it works, use of this approach may be limited to manmade sites such as mines.
That’s because scientists want to guard against unintended ecological effects that may come along with introducing a new organism into a cave setting. Given the state’s mining heritage, though, there are many abandoned mines in Wisconsin used by bats. Three of the largest hibernation sites in the state are mines, White says.
Bat populations are not evenly distributed throughout the state, so finding a way to treat bats at the largest hibernation sites could make a huge difference. Out of the 150 sites identified by the DNR, 90% to 95% of the state’s known bat population congregates in just three of them, White says.
The fungus has been found at all three locations, says Owen Boyle, DNR species management chief. These sites are still in the early stages of infection, though, so researchers haven’t seen mass mortalities yet.
With fewer bats left surviving after each winter, scientists know they don’t have much time to save Wisconsin’s bats. “Everybody is looking for an answer, whether it’s a silver bullet or something to buy time,” White says.
The one good thing to come out of the deadly disease is improved public perception of bats. Seen silently flapping overhead at dusk, bats provide important pest control, consuming their weight in mosquito-sized insects each night.
“The education and awareness, and the outreach that has come from this terrible, terrible disease has helped out a lot,” says White. Public interest in the bats’ plight has inspired 1,500 volunteers to help track populations.
Another way people can help is by putting up bat houses. While these don’t offer sites for hibernation, they do provide valuable shelter for bats at other times of the year. During fluctuating spring temperatures bat houses provide protected daytime shelter (ideally positioned to receive 6 to 8 hours of sunlight), so the bats can stay warm and conserve energy. Having such respite may allow a bat to clear an infection, if it hasn’t yet become critical, White explains.
If bats are able to avoid disease and other threats their longevity is remarkable. The DNR found a bat estimated to be 32 years old.
