Artificial Bat Cave: A Radical Idea to Save America's Bats

Why We Need to Build It

Cory Holliday explains why the artificial cave could hold the key to saving America's bats.

View the video.

►Hear the NPR report on the cave.

►Read the New York Times story on the cave.

►See inside the artificial cave with the CBS Evening News.

►Researchers find a promising treatment for bats with white nose syndrome.

►Learn more about bat houses and how to build your own.

by Paul Kingsbury

To fight white nose syndrome, an epidemic that is causing catastrophic die-offs in America’s cave bat populations, The Nature Conservancy in Tennessee has embarked on a radical idea.

Building an artificial cave next to an existing natural bat cave in Tennessee. The artificial cave can be disinfected of the tell-tale white fungus that causes white nose syndrome—thus creating a healthier haven for bats.

Following expert scientific review of the building plans, The Nature Conservancy began construction on the artificial cave in August 2012 and finished construction in early October to allow bats to take up residence that winter.

Nature.org talked with Cory Holliday, cave and karst program director for The Nature Conservancy in Tennessee.

The artificial bat cave prototype was built in 2012, and, as of 2017, bats have not hibernated in it in great numbers. However, researchers say that it can take years for bats to choose a new location for hibernation. In the meantime, we are exploring research projects to conduct at the artificial cave.
"It's a little like Field of Dreams: If you build it, they will come. Past experience shows that bats are constantly seeking new habitats."

Cory Holliday, director of the Cave & Karst Program for the Conservancy in Tennessee


Why build an artificial cave?

Cory Holliday:

White nose syndrome has been devastating to cave-hibernating bats since it was discovered in New York state in 2006.

We’ve lost more than 5 million bats in 19 states
[as of 2014: we've lost more than 6 million bats in 25 states], and we still haven’t identified any way to control bat mortality rates or the fungus that causes those deaths. Up to this point we have simply had no tools to employ to keep bats from dying. And a loss of bat species could have serious consequences for people. Bats are the number-one predator of night-flying insects. One million bats can eat 694 tons of insects per year. A recent study estimated the value of bats to Tennessee agriculture at over $313 million annually.


Building an artificial bat cave seems like a pretty wild idea to address the problem. Where did the concept come from?

Cory Holliday:

In June 2010, I attended a U.S. Fish and Wildlife Service-sponsored workshop with cave and bat experts on keeping and breeding bats in captivity to protect them from white nose syndrome. The idea came out of a small working group session. And these bat experts thought it might have the potential to save large numbers of bats.


What is the artificial cave going to look like?

Cory Holliday:

It will be long and rectangular--about as big as a single-wide house trailer—only taller with 11 foot ceilings. That’s 78 feet long. And the structure will be buried in a hillside near an existing natural bat cave.

Initially we thought we would build this cave out of spray-on Shotcrete and have it all formed in a single unit. But we recently found a much more affordable design, adapting huge rectangular waterway culvert pieces that we will attach together like building blocks. This modular design will save us money and construction time. And it will be easier for other groups to replicate it elsewhere.


What makes you think the bats will use this artificial cave?

Cory Holliday:

It’s a little like that Field of Dreams movie: If you build it, they will come. Past experience shows that bats are constantly seeking new habitats. They move from cave to cave, tree to tree, always looking for new places that meet their needs for roosting and hibernating.


Has an artificial cave ever been built before?

Cory Holliday:

Not for cave-hibernating bats and not to address white nose syndrome. Artificial roosts have been built that simulate hibernating roosts in trees for Rafinesque big-eared bats. In fact, we’ve built them successfully in Tennessee to replace lost habitat for the Rafinesque bats, using plans from Bat Conservation International.

And then there is a fellow in Texas who built an artificial roosting cave for Mexican free-tailed bats. It’s been a great success. When he started, folks thought he was crazy. But the bats are there in great numbers today.


How do you entice the bats into the cave?

Cory Holliday:

It’s all in the design. In order for a cave like this to work it has to be a cold air trap. It has to be underground. The ceiling has to be farther below ground than any entrance to create that cold air trap. It has to have air flow through two entrances, and the entrances have to be at differing levels, because the flow of air is much like the thermodynamics of flowing water. Using a specially structured ventilation damper, we can adjust that air flow to fine-tune the climate.

Keep in mind that this artificial cave is located very close to an existing bat cave that has hundreds of thousands of bats. It's within a few hundred feet of the existing cave.


How many bats live in the natural cave on the site?

Cory Holliday:

Historically about 40,000 to 50,000 bats used that cave. After The Nature Conservancy bought it in 2006 and fenced it to keep out vandals, the numbers have skyrocketed. In 2010, we counted 160,000 using thermal imaging and computers. This summer we counted 265,000.

Unfortunately, we found white nose syndrome in gray bats at that cave this past winter. If the disease follows the typical trend, then we could see 90 percent mortality at that cave in three years. So the clock is ticking on us.


What happens if the bats don’t go in the cave?

Cory Holliday:

The bats should go in as long as we get the temperature and humidity right. We believe they will. If they don’t go in, then we must have done something wrong, and we would make any adjustments we can.

In addition, we plan to play recordings of ultra-sonic bat calls at the artificial cave when it first opens to entice bats to check it out.

But if the bats just wouldn’t go in, then we could use the cave as an on-site laboratory to study bats that we brought in. Unfortunately, the gray bats of the natural cave we plan to build next to are a federally listed endangered species, and we probably would not be allowed to move gray bats without a permit.

Or we could work on toxicity trials with anti-fungal agents and test them on cave micro-organisms that we would bring in. The thing is, we know of anti-fungal compounds that will kill the Geomyces fungus that is associated with white nose syndrome. Unfortunately, those chemicals, in the wrong concentrations, also kill many other cave life forms, including microorganisms.

So a place that mimics a natural cave environment would be a very useful laboratory for testing these anti-fungal agents on other cave-dwellers, which don’t survive so well in traditional laboratories.


How much does an underground house for bats cost?

Cory Holliday:

Ours is right at $300,000. We don't have all the funds in hand, but we are moving ahead with this project. The bats don't have time for us to wait another season.

Paul Kingsbury is a conservation writer for The Nature Conservancy in Tennessee.


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