11 facts about Minnesota bats and a mystery plague that threatens them

CC/Flickr/U.S. Fish and Wildlife Service Southeast Region

A little brown bat exhibiting symptoms of white-nose syndrome.

On a beautiful winter’s morning last Saturday I drove north to St. Croix Falls for a program on white-nose syndrome, joining more than 60 other citizens concerned about this threat to Minnesota’s bat populations.

This is a topic I have been interested in, but had not gotten around to studying, since a visit to Wind Cave National Park in South Dakota in the fall of 2012, where we were questioned closely at the welcome center about any visits we might have made to other caves or mines in the previous five years.

This longevity of the white-nose fungus spores was impressive, as were the awful statistics about mass bat die-offs in the eastern United States. Then came the news last August that the fungus, recently renamed Pseudogymnoascus destructans, had turned up on bats in Minnesota.

Here are the 11 most interesting things I took away from Saturday’s talk by Gerda Nordquist, the Minnesota Department of Natural Resources‘ bat specialist (and from some further reading she inspired me to do), starting with the few bits of good news:

1. The fungus doesn’t always bring immediate catastrophe. Although Pseudogymnoascus was found in swab tests on bats at two Minnesota locations — Forestville/Mystery Cave State Park near the Iowa border, and Soudan Underground Mine State Park near the Canadian border — bats in those places did not show signs of the disease itself (contrary to some early news reports).

Nor were fungus spores found elsewhere in these caves.

For reasons that remain unclear, not all bats exposed to this skin-eating fungus will develop the syndrome’s horrific lesions on their nose and wing tissues. At sites in Vermont and Missouri, bats have remained disease-free for four years or longer in the presence of the fungus.

Although white-nose syndrome is known to have killed as many as 7 million bats since 2006, with mortality rates over 90 percent in some infected caves, even bats that are seriously weakened by the syndrome will sometimes recover after emerging from hibernation.  (Pseudogymnoascus is a cold-loving fungus and afflicts bats that overwinter in caves, mines, sewers, culverts and similar locales; migrating bats appear to be unaffected.)

And in Europe, species essentially identical to the North American types being decimated by white-nose syndrome disease are untroubled by the fungus, possibly because they co-evolved with it.

2. Still, the trend lines are awful. Since 2006, when white-nose syndrome was first detected in a cave near Albany, N.Y., the fungus has been found in 22 states and 5 Canadian provinces, and bats have developed the syndrome in all but three of these. (So far the fungus has skipped over Wisconsin, a peculiarity a fellow Wisconsinite in the audience attributed to our governor’s repellent properties.)

The U.S. Fish and Wildlife Service is predicting regional-scale extinction of the little brown bat within as little as a dozen years. The little brown bat, big brown bat, northern long-eared bat and tri-colored bat are the Minnesota species at risk from white-nose syndrome; the non-hibernating, migrating species — hoary, red and silver-haired bats — are not afflicted.)

3. Some migrating bats in Minnesota winter as far afield as Mexico, according to banding data.

4. Bats make cool, almost musical sounds with their radar rigs. In addition to the chirping we can hear without special gear, the ultrasonic clicking sounds made by bats for purposes of echolocation can be rendered audible to the human ear with electronic equipment that Nordquist and her researchers use to count and track bats.

She played a clip of an echolocating big brown bat that sounded to my amazed ear like a Caribbean percussionist; you can find a similar sample here.

Bats clearly listen for one another as they navigate a summer insect swarm, Nordquist said; whether they endeavor to call out in this way is not known.

5. Bats are important to ag systems, not just ecosystems, in ways that go well beyond their oft-discussed role as important pollinators.

Some 70 percent of bat species, including all those in Minnesota, are insectivores and consume massive quantities of insect pests. Nordquist quoted one set of calculations holding that bats may save Midwestern farmers between $3.7 billion and $5.3 billion a year in avoided pesticide costs.

They are also excellent dispersers of seeds.

6. However, ag systems may not be as kind to them. Of all the bright questions from Saturday’s audience, perhaps the most insightful was whether pesticides might be rendering North American bats newly vulnerable to the Pseudogymnoascus fungus, in the way that certain insecticides may be making honeybees suddenly more vulnerable to parasites they have endured for decades.

That’s a subject that needs more research, Nordquist said, but it’s certainly a strong possibility. Patterns of white-nose syndrome look very much like those of an immune-suppression disease,  and insecticides have been known to promote these in other species.

7. Breeding disease-resistant bats isn’t a solution, Nordquist said in answer to perhaps the dumbest question from the audience, advanced by your correspondent, still thinking about the honeybees.

The selective breeding techniques being explored as a way of getting honeybees past colony-collapse disorder can’t really work with bats because “they resist captive breeding,” Nordquist patiently explained. Also, they don’t live in hives, and are difficult to herd.

8. That decontamination foam you have to walk through to visit a bat cave these days? Woolite! And it does kill Pseudogymnoascus spores, Nordquist said.

However, it remains highly unclear how the spores are spread from cave to cave, so getting tourists and spelunkers to decontaminate their boots and clothing is more of a common-sense precaution than a proven quarantine strategy.

One other — and heartbreaking — possibility is that bat researchers have been transmission agents, too.

9. New research holds out hope of controlling Pseudogymnoascus with biological agents, including a project at Georgia State University to see if a naturally occurring bacterium can be used to fight the bat-killing fungus without introducing all the risks associated with chemical fungicides.

Indeed, Nordquist said, one possible explanation for disease-free bats in places like the Soudan mine, as well as the Vermont and Missouri hibernacula, is that some other organism is exerting helpful biocontrol.

10. In the meantime, there’s little that governments and citizens can do to help the bats.  Re-opening bricked-up caves along Minnesota rivers isn’t a good option, Nordquist said in answer to a question, because it’s hard to come up with a barrier that lets the bats in but keeps the vandals out.

“Closing off a cave with gates is a gauntlet the vandals just love to take on,” she said. “They spend incredible amounts of energy to defeat our gates. And caves are dangerous places.”

11. But if you should happen to see a flying bat this winter, report it to the DNR, because it’s mostly likely a hibernating bat that has been roused by some annoyance — and that annoyance could well be white-nose syndrome.

* * *

Saturday’s presentation was the first in a spring series sponsored by the St. Croix River Association and the National Park Service.

Resources for further inquiry:

• Minnesota DNR’s main page on white-nose syndrome.
• The home page of WhiteNoseSyndrome.org, a large collaborative of federal agencies, state agencies, universities and others.
• The white-nose syndrome page of Ontario’s Ministry of Natural Resources.
• A great, eight-minute video on bats at white-nose syndrome is here.