Quick — To the Bat Cave!

Dying to go inside a bat cave?

Nature.org spoke with Cory Holliday, director of The Nature Conservancy’s cave research and protection efforts in Tennessee, about bats and bat caves. With more than 9,600 documented caves, Tennessee is home to the highest number of caves in the country. Holliday set our bat-fears to rest — and gave us the scoop on what it’s like to hang out with these fascinating creatures.
"Bats are often misunderstood. . . . They eat many of the insects we consider pests."

Cory Holliday, director of The Nature Conservancy’s Tennessee Cave Program


Bats form large colonies inside caves — when you go in, does it feel creepy, or does it feel like you're crashing a party?

Cory Holliday:

You definitely get the feeling that you don’t belong. If it is a summer colony, the bats are very active and it often seems to be raining bat guano. Much like the bar scene in National Lampoon’s Animal House, you’re crashing a party you wish you hadn’t.

In the eastern United States, bat colonies can be upwards of 500,000 bats, and in the southwest, there can be millions of Mexican free-tailed bats in a single cave. But in general, the size of bat colonies has decreased as cave habitat has been altered.


What other kinds of creatures do you see down there?

Cory Holliday:

Cave environments are fairly diverse. Some higher cave passages can be extremely dry and reminiscent of a lunar landscape — very dusty and seemingly barren.

Others have nearly 100 percent humidity and support obvious food webs with crickets, bacteria, molds, millipedes, spiders, pseudoscorpions, salamanders, crayfish and all sorts of creatures.

Many cave animals are blind and without pigment, so they rely on defense mechanisms other than camouflage. For instance, the tetracian millipede excretes a very stinky oil that is so strong it fills the entire cave with its smell.


Got any good bat cave stories?

Cory Holliday:

At summer bat caves, we monitor the number of bats by using night vision and manually counting the bats as they exit the cave at night. One night we were setting up with our night vision scope in a spot where we would have good visibility of the bats exiting the cave.

Like other animals, when bats awake and get active, they need to lighten their load and empty their bowels. It turned out that I had inadvertently placed myself directly below the flight path on the cave's bottom entrance rim, in a position that required I look up to get the count I needed.

This particular cave housed a huge population of Gray bats that spent over 45 minutes exiting the cave in a steady stream of up to 20 bats per second. While the bats exited the cave after a long day's nap, I did my best to count them through a nasty shower that left me far dirtier than when I started.


Ewwww! So what makes a good bat cave?

Cory Holliday:

Bats are every bit as diverse as humans and so are their living conditions. But typically, a good bat hibernation cave has multiple entrances — with at least one large entrance — and multiple levels to promote airflow.

Hibernating bats generally seek out areas of the cave that are as cold as their bodies will tolerate. The warmer the hibernating temperature is, the higher the bats’ metabolic rates and the more energy required to sustain them through the winter. 

Summer bat colonies seek out caves with stable temperatures that are warm enough to rear young but not so warm that they need to use excessive energy to maintain body temperatures.


How do the bats find their way back after night is over?

Cory Holliday:

Bats have complex spatial memories and directional senses that aren't entirely understood. Research has shown that bats can be taken from a cave, transported 200 miles away, and return to their home cave within a few days. Actually, finding their way back to the cave after a night of feeding is nothing compared to finding their own pup among hundreds of thousands of other pups.


Do generations of bats live in the same cave, or do they seek new caves from time to time?

Cory Holliday:

This is something that is being actively researched, but the simple answer is yes. Female bats do return to the caves where they were raised in order to rear their own young, and they usually return to the same hibernation site year after year — unless cave conditions change, which is often due to humans accesssing the cave.


Are such changes the biggest threat to bats?

Cory Holliday:

Yes. Like many other organisms, the biggest threat to bats is the loss of suitable habitat.

Bat caves suffer from increased human activity and altered airflow. Often caves are partially flooded by dammed rivers and streams. Sinkholes frequently get filled and cave entrances get blocked or closed off by landowners who don’t want the human cave visitors, but are often unaware of the life within a cave.

Even before human disturbance, the majority of bats lived in a small percentage of caves that had the ideal conditions. Now they have been pushed out of many of those caves and rely on caves with marginal conditions or caves that are not able to support the same high numbers of bats. Because both humans and bats prefer large, complex caves, bats that are the most reliant on caves are also the most endangered.


What's The Nature Conservancy doing to protect bat caves?

Cory Holliday:

Since the vast majority of caves are on private property, The Nature Conservancy works with landowners to help them better understand and manage the life in their caves. We also work with partner organizations and agencies to develop concerted efforts to fill the gaps in bat conservation. Both The Nature Conservancy in Tennessee and The Nature Conservancy in Alabama have been awarded Landowner Incentive Program grants to help landowners manage and protect cave species.


It's Halloween, and people are generally afraid of bats anyway. Are you saying we have no reason to fear them?

Cory Holliday:

Bats are often misunderstood. If they're dive-bombing your head, it’s because they are attracted to food. But not to worry — you’re more likely the bait than the food; they eat many of the insects we consider pests. In fact, bats can eat nearly their own weight in insects in one night.

Bats are important to humans because they keep pests like mosquitos under control and they help pollinate many crops, including bananas, mangoes, figs and cashews. On the other hand, like many other animals, bats do carry rabies and should never be handled by someone unvaccinated, or without a scientific purpose. 

Cory Holliday has worked for The Nature Conservancy since 2004 and directs the Cave and Karst Program for The Nature Conservancy in Tennessee. Much of his time has been spent documenting and monitoring globally rare and threatened cave-dwelling organisms. Holliday has helped find dozens of new species and even had one named after him — Pseudotremia hollidayi, a cave millipede found in only one cave. Holliday is part of a multi-organization team of biologists who monitor and actively protect bats by restoring habitat and reducing human impacts on cave systems.


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