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Issues of the Environment: White-nose syndrome threatens Michigan's bat population

Dr. Allen Kurta visiting Keel Ridge Mine in Iron Mountain, Michigan for research.
Dr. Allen Kurta
Dr. Allen Kurta visiting Keel Ridge Mine in Iron Mountain, Michigan for research.


  • The fungus responsible for White-nose Syndrome (WNS) arrived in Michigan in 2014, and Dr. Kurta began documenting the devastation that year, finding bat numbers were down 40-60% in parts of the state. 
  • Tricolored bats, a small species that is present in southeast Michigan, have been especially hard hit. Once a colony of tricolored bats is infected, the disease causes declines of more than 90%, officials said. In September 2022, the U.S. Fish and Wildlife Service chose to list tricolored bats as endangered. This is the second bat species listed this year; the northern long-eared bat was changed to endangered in March.
  • Bats are ecologically and economically significant in Michigan, controlling pests like the emerald ash borer and corn earworm moth. According to the United States Geological Service, some studies estimate that pest control service from bats is worth over 3.7 billion dollars per year, and possibly as much as 53 billion dollars per year (Source: https://www.usgs.gov/faqs/why-are-bats-important). Although WNS is the primary concern they are also at risk from climate change and habitat loss. 
  • Endangered status makes it illegal to take the bats or the trees where they raise their young, exclude them from roosting in buildings where they have taken up residence in a way that harms the bats or kills them, to collect and transport the species and to use biological control agents against them at any life stage. Dr. Kurta says that the locations of many of the trees where bat maternity colonies are located are not mapped, so untold numbers are likely to still be at risk.
  • As the weather grows colder bats in our listening area (primarily the little brown bat which Kurta has found to be quite affected by WNS) may accidentally enter dwellings, and there is a small risk of rabies if bitten. However, humans are a greater threat to bats, and as they become more imperiled care should be taken to preserve them when it is necessary to remove colonies from the home.
  • Dr. Allen Kurta is biology professor and biology professor from Eastern Michigan University who has been studying bats in Michigan for decades. He says that white-nose syndrome is the most devastating wildlife disease ever in North America. He points out that tricolored bats tend to roost and hibernate alone or with just a few others, so habitat protection on a broader scale is not an effective strategy for conservation of this species. According to the Detroit News, “A fix doesn't appear close, said Kurta, who attended a meeting of specialists in June. Among many ideas are using ultraviolet light and chemicals to kill fungus spores or limit their spread, he said, but it would be hard to apply them in the many sites where bats roost and hibernate. Scientists also are trying to develop a vaccine. Most of the affected bat species give birth to only one or two offspring a year, meaning their recovery will require many years even if the disease is controlled, Kurta said.” (Source: *directly quoted* https://www.detroitnews.com/story/news/environment/2022/09/13/tricolored-bat-endangered-white-nose-syndrome/10368031002/)


David Fair: This is 89 one WEMU, and a vital part of the health of our ecosystem is increasingly threatened. You may not love to see them in your house, but the loss of bat population can give us significant ecological and economic impact on our lives. I'm David Fair, and welcome to this week's edition of Issues of the Environment. In September, the U.S. Fish and Wildlife Department officially listed the tri-colored bat as an endangered species. The culprit: a fungus that causes what's called white nose syndrome. Colony exposure can cause a 90% or more population decline in tri-colored bats, and it is the second bat species to be put on that endangered list this year. The other being the northern long-eared bat. Well, our guest today is one of the nation's leading bat experts and happens to be a biology professor at Eastern Michigan University. Dr. Allen Kurta has been on top of the issue of white nose syndrome in Michigan ever since it first arrived in our state in 2014. Dr. Kurta, thank you so much for the time.

Dr. Allen Kurta: Good morning.

David Fair: First of all, there are a lot of folks that find bats a little bit creepy and like to avoid them, if at all possible. You get right up in there and are hands-on. What landed you in that place? What's the fascination?

Dr. Allen Kurta: Oh, my Lord! What a question! There are so many neat things about bats. It would take forever. You should come to one of my public talks. But, you know, the smallest mammal in the world is a bat. They echolocate. They have the largest babies of all mammals, the equivalent of a 100-pound human female giving birth to a 22-pound child.

David Fair: You just made about half the population cringe.

Dr. Allen Kurta: Yeah, yeah, yeah. Oh, and they're the longest lived mammals in the Great Lakes region. They live up to 34 years in the wild. It's just amazing for such small creatures.

David Fair: Well, we should all be glad that we have someone so interested in and appreciative of bats. As I mentioned, white nose syndrome was first discovered in Michigan in 2014. As you began researching impacts in that first year, did you recognize the existential threat it had to bat colonies?

Dr. Allen Kurta: Well, only because we had heard what was happening in the east, in the northeast in particular. So, that disease arrived in New York state in 2006, and it took eight years for it to finally make it to Michigan. So, we had an idea of what was coming.

David Fair: And over the past eight years, how much further west has it spread?

Dr. Allen Kurta: I just looked at the map this morning, and there's only about four states in the lower 48 that are not having that fungus: Florida, Oregon, Nevada, and Arizona, I believe they're the only ones.

David Fair: What is this particular fungus that wreaked such havoc, and where did it come from?

Dr. Allen Kurta: Well, it came from Europe, so it is present. It's been in Europe probably for tens of thousands of years. And it came over either on the boots, maybe, of a researcher or a tourist. And the spores of that fungus got deposited in a cave--a commercial cave--that offers tours near Albany, New York. We call it a psychrophilic or cold-loving fungus. And that's because it does not grow at temperatures above 68 degrees Fahrenheit. So, it's not something that people have to worry about or cats or cows or dogs, etc.. But it does grow in cool temperatures, and it grows on the skin of bats. So, the hairless skin of bats--their nose, their forearms, their feet, their ears, etc. It attacks the skin, causes great damage, increases water loss. And one of the most important things is it doubles the frequency of arousal by these bats from hibernation. And 90% of all the fat that an animal stores in fall to get through hibernation is used to fuel periodic arousal from hibernation that normally occur about every two weeks. But when they become infected, they arouse about once every week, and they use up that fat twice as fast. And they run out of it in December, January, February. And that's long before there's any flying insects around, so they end up dying of starvation.

David Fair: WEMU's Issues of the Environment conversation on the decimation of bat populations continues. Our guest is EMU bat expert and biology professor Dr. Allen Kurta. Now, whatever opinion people have on bats, there is overwhelming evidence of the benefits they provide. Mosquito populations would be much higher. The bats help control pests, like the emerald ash borer and earworm moth. Additionally, because people generally don't like to deal with bats themselves, the United States Geological Survey says pest control services are worth at least $3.7 billion in pest control, perhaps as high as $53 billion to the economy on an annual basis. Why else are bats so important to us, Dr. Kurta?

Dr. Allen Kurta: Well, you have to understand that about 20 to 25% of all mammalian species on Earth are different kinds of bats. So, they're a very abundant, very diverse group. They're important in keeping down the agricultural paths, but they also eat insects that potentially transmit diseases to humans in the tropical areas. They pollinate plants. And they're very important for distributing seeds in tropical forests.

David Fair: There are so many species of bats throughout the world. What are the most common in Michigan and here in Washtenaw County?

Dr. Allen Kurta: Well, we have nine species in the state. The most common in the southern part is what's called the big brown bat. And if you have a colony of bats in your barn or in your house, there's probably a 95% chance that it's that species. The next most common is one that very few people ever see, and it's the eastern red bat. It differs from the big brown in that it doesn't live in buildings. Instead, it's just a single individual that hangs up among the leaves of the tree.

David Fair: Since white nose syndrome appeared in Michigan in 2014, have you been able to adequately assess what the overall impact has been on the bat population?

Dr. Allen Kurta: Oh, yes, unfortunately. So, along with Steve Smith from Iron Mountain, I've been doing surveys of the bats in their high vernacular in the western U.P. for 25 years. Where these bats hibernate are underground sites. They're abandoned copper and iron mines, primarily. And based upon the data that we had before the disease arrived and since it arrived, we can tell you that the overall population in the western U.P. has declined by 89.9%.

David Fair: That is a huge number.

Dr. Allen Kurta: It's just staggering. The one that comes to mind is the Mead mine, which is right off the highway, on the road and going to Lake of the Clouds and the Porcupine Mountains. That mine had 17,700 bats. And after white nose syndrome, it had 92.

David Fair: Has there been any advancement in figuring out how to better protect bats from the insidious white nose syndrome?

Dr. Allen Kurta: Well, you know, to a large degree, I think it's too late because it has expanded across the continent. There are lots of things that are people are still trying, but, in my mind, they're not too practical because they may work on a small scale and a very small site. But, you know, in Michigan, we had seven populations that were greater than 10,000 animals, and they were all in very large underground mines. And so, if you're going to spray a chemical, for example, that would kill the spores of the fungus during the summer, no one's going to pay for a one-kilometer length of a mine to be totally sprayed from ceiling to floor. So, the fungus is here to stay. Definitely.

David Fair: This is 89 one WEMU. And again, we're talking bats with Dr. Allen Kurta. He's a leading expert on bats and serves as a professor of biology at Eastern Michigan University. As we enter the cold months of the year around here, like people, bats often seek out warm places to nest. That sometimes means our chimneys in our attics. We certainly don't want to further impact the population by killing them off. What's our best course of action?

Dr. Allen Kurta: As far as white nose syndrome?

David Fair: Well, about protecting the populations in whole.

Dr. Allen Kurta: Well, I think education is a key thing. If people understand that the bats are not all rabid and they're not aggressive and they don't attack people and that they do perform good, then, if you change those attitudes, then people are going to be more tolerant of them. And there's nothing wrong with not wanting bats in your house, but there are humane ways of excluding them from the building that should be pursued rather than something that's going to kill the animals.

David Fair: So, again, returning to white nose syndrome in specific, if we don't get this under control, and it sounds like in your opinion, we're unlikely to do so, what is the global bat population going to look like, and what is the bat population of Michigan going to look like a decade down the line?

Dr. Allen Kurta: Well, in Michigan, I think it's going to stay low for these particular species. So, out of the nine species of bats, this is primarily affecting three or four of them that roost underground in mines and in caves in the state of Michigan. We do have four other species, for example, that are long distance migrants. They will primarily leave Michigan and fly south of the Ohio River Valley and hibernate in warmer climates. And they do not seem to be affected by white nose syndrome. So, some of our bats are going to decrease. They have decreased. This 90% decline is very similar to what is has been observed in the east. And so, I think that we're leveling off at this 90% level. And whether it increases a little bit in ten years from now, I don't know. But it will not increase quickly because the majority of bats that are being impacted only give birth to a single offspring per year.

David Fair: Well, that is not necessarily good news. The impacts will reverberate in a variety of ways throughout the state of Michigan and wherever white nose syndrome is impacting bats. Thank you so much for taking the time today and sharing the information with us, Dr. Kurta.

Dr. Allen Kurta: Thank you.

David Fair: That is Allen Kurta, leading expert on bats and professor of biology at EMU. For more information, go to WEMU dot org. Issues of the Environment is produced in partnership with the office of the Washtenaw County Water Resources Commissioner, and we bring it to you each Wednesday. I'm David Fair, and this is your community NPR station, 89 one WEMU FM.

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