Defenders Magazine

Keeping Bats in Mine

Old mines provide new hope for an endangered bat in Illinois.

By Heidi Ridgley

© U.S. Fish and Wildlife Service

The voice I'm following sounds hollow in the still underground air: "I got eight pips, two long-eared, two big browns and an Indiana." A chamber away a reply rings from the darkness, "What he said, plus four more pipistrelles--oh, and watch the guano."

I stand gawking at a brown, dew-soaked bat clinging to the mine wall. The droplets on the fur of this pocket-sized creature--an eastern pipistrelle or "pip"--glimmer like crystals in my headlamp. I quietly tear myself away not wanting to disturb the animal's winter slumber, but my stealth steps are in vain. "As soon as we entered this mine, they heard us," says Tim Carter, a Southern Illinois University biologist whose voice leads me forward. "Even though they're hibernating, their ears still work."

Carter, his two assistants and I are winding through the corridors and cavernous offshoots of a 20-acre abandoned silica mine about a half-hour's drive south of Carbondale, Ill. The researchers are logging each bat they spot--from the more common big browns, little browns, northern long-eareds and pips to the endangered and rapidly declining Indiana. But it's more than an academic study: Mine owner Unimin Speciality Minerals, Inc. holds about 50 other abandoned mines in the area, many of which are now occupied by the furry nighttime fliers. In the last decade, the mines have become one of the most significant havens for rare Indiana bats in Illinois, prompting conservationists, state and federal officials and Unimin executives to make these shelters as hospitable to these bats as possible.

"Some believe that the loss of the species' summer habitat--the farmlands of the Midwest--has contributed to the population's decline, but mining and commercialization of caves have left Indiana bats with a critical shortage of hibernation sites," says Merlin Tuttle, president of Bat Conservation International (BCI) in Austin, Texas. "What we've found is that if you can give them back an ideal hibernation site, instead of continuing their decline the bats immediately begin to recover."

Of the approximately 4,600 mammal species on the planet, more than 900 are bats--the only mammals that can fly. Because they do it at night, they've become victims of the irrational fear humans have of darkness and the unknown. Bats are maligned as demons, hopelessly associated with Dracula and blamed for passing rabies--even though getting hit by lightning is more likely. The truth is that bats greatly benefit humans.

Depending on the species, bats are either busy pollinating flowers and spreading seeds or devouring bugs. In North America, home to 47 bat species, almost all bats are insectivores. As primary predators of night-flying insects they can consume up to their own body weight in bugs in an evening, which means a colony of 1,000 bats can easily snatch millions each night. "Bats are just as important by night as birds are by day," says Tuttle.

Indiana bats--named after the state where they were first identified--were once so abundant in the East and Midwest that a single cave might hold millions in winter. Only about 450,000 Indianas remain today, and experts fear that loss of hibernation sites, pollution and human disturbance could spell the species' doom. Research like that being conducted by Carter and his team is crucial to the bats' survival.

"I can see an ear from here," says Brad Steffen, Carter's graduate student, pointing his flashlight toward a small brown blob about three-quarters up the 20-foot wall. "That one's a long-eared." He turns and slides down a 15-foot pile of white powder and disappears again, except for his voice. "This is where counting is going to get more difficult--they're hanging from 40-foot ceilings in here." What makes it a little easier is the backdrop. The mine's walls are pure white, made of a fine quartz sand--microcrystalline silica--that is used in a variety of products from pool chalk to paint. But after three hours today in the mine called Birk 2 and the tallying of 1,946 bats, only 28 are Indianas. "In this case, it's actually a good thing," says Carter. "We don't want to attract bats to this mine long term."

Unlike other Unimin mines, Birk 2 still has material left in it that could be extracted, and although the company turned to surface mining in the mid-1980s, it might later decide to reclaim this one. So Unimin allowed Birk 2 to become a short-term bat experiment. The goal was to find out what attracted the bats in order to replicate those conditions in other, permanently abandoned mines and to then make this particular mine inhospitable to Indianas after the experiment was over. "When we thought the temperature wasn't right for Indiana bats in Birk 2, for example, we moved a houseful of dirt to block an entrance," says Carter. After proving this stabilized the temperature and attracted the bats, they reopened the entrance the next summer to discourage the species' fall arrival.

Different from other bats in this mine, Indianas can't withstand much temperature fluctuation. Ideally conditions must hover between 38 and 43 degrees Fahrenheit. Carter believes this sort of sensitivity is one reason why the Indiana bat is an endangered species while the others get by a little better. But securing the bats' future goes beyond climate control. "Some abandoned mines might have just the right temperature, but it won't matter if we can't stop people from going into them," says Carter. "More than a few disturbances a year speeds up the bat's metabolism too many times, causing it to run out of juice half way through winter." If a bat wakes up too soon--before bugs are back--it will starve to death.

To prevent explorers, carousing teenagers and vandals from entering the mines, Carter is working with Unimin and the Illinois Department of Natural Resources (DNR) to install specially designed steel barriers with grates at some mine entrances. The massive gates keep people out but allow bats to fly free. The structures can also keep an entire hillside from collapsing--and they are designed to last at least 100 years.

The next gate installation is scheduled this summer for Mine 30, home to as many as 3,600 Indianas and more than 1,000 bats of other species. "This is the second largest colony of hibernating Indiana bats in southern Illinois--and the entrance is decaying," says Carter. Building the tunnel and gate--funded by the U.S. Fish and Wildlife Service, the Illinois DNR and the Shawnee National Forest--will cost about $30,000. Unimin, which recently relinquished the mine after working it to capacity, will also provide heavy machinery and much of the labor.

At nearby Jason Mine, which Unimin permanently abandoned in the 1960s, such gate construction took on special urgency last summer. "At almost every one of the Indiana bat mines, numbers were going up," says Carter. "The exception was Jason Mine, which dropped from 87 bats to 24." Thinking that the crumbling entrance was causing temperatures inside to rise, Carter bumped it to the top of the list for entryway stabilization and gate installation. In the process, he noticed a box of empty .22 shells. The next year bat numbers were back up. That's also when he noticed that what looked like a pile of leaves and sticks tucked into a crevice was actually about 60 bat carcasses. "Our decline wasn't because of the entrance but because someone had used bats for target practice," says Carter. "Now that will never happen again."

Unimin's Magazine Mine, encompassing 21 acres and descending several hundred feet below ground, shelters the fastest-growing population of hibernating Indiana bats anywhere--thanks largely to a bat gate installed there in 2001 with help from BCI and the Illinois DNR. In 1999, surveys reported only about 9,000 bats. In 2005, some 33,000 Indianas hibernated here. Such quickly rising numbers can't be attributed to reproduction alone.

Researchers believe bats either stumbled upon the mines during migration or that there's some type of communication happening between females in their summer breeding grounds, which stretch from Michigan to central Alabama and over to the Carolinas. "If one female shows up plump while the others look like they merely survived winter, they might interpret that the fat and healthy bat found a ‘Holiday Inn' and decide to join it the following year," says Carter.

While biologists are delighted to have the bats in southern Illinois, they do have some hesitations about luring more, given that the long-term stability of the mines is unknown. To that end, Carter is working with the DNR to hire a graduate student to study the rate of collapse. "We suspect that cave-ins are not much of a worry," says Joe Kath, endangered species project manager for the DNR. "I've been in these mines numerous times, and while I've seen a 10- or 20-foot section of wall down, there's never been full chambers closed off. A cave-in could crush some animals, but it's a very small price to pay considering the overall benefit these mines provide to the entire species."

The bigger worry is putting all the "bats in one basket." From the rapid increase in the population of Magazine Mine alone--expected to hit 50,000 in the next few years--it's clear Indiana bats think they've found an underground safe house. "But what if we create two more mines like it?" worries Carter. "Realistically, we could have 200,000 Indianas in southern Illinois." While he admits that it would be a dream come true for him, to lure 50 percent of an endangered population to one place is also problematic: A disease or catastrophe could wipe them all out. "This area is obviously going to be an important spot for Indiana bats," he says. "How far we go to attract them here is yet to be determined."

Undaunted by bats, senior editor Heidi Ridgley did have to fend off claustrophobia while gathering material for this story.