By Clyde Outside
Some evenings are built for spectacle. You know I’m not the flashy, ticketed kind, but the quiet, living kind. On a recent summer night, I found myself paddling across the surface of Nickajack Lake toward a shadowy bluff. In my usual Clyde Outside fashion, the kayak slid off the roof of the Hondaminium, and I seal-launched from the wooden dock with plenty of light left to navigate to my destination of the Nickajack Cave, home to one of the most remarkable biological events in the Southeast.
A Cave, a Lake, and an Unexpected Union
Nickajack Cave was once a dry cavern that extended deep into the limestone ridges of the Cumberland Plateau. But in 1967, the Tennessee Valley Authority completed Nickajack Dam, flooding the lower chambers of the cave and creating what we now call Nickajack Lake. This wasn’t just a change in topography, it was a shift in ecological history.
The cave is carved into Mississippian-aged limestone, part of a karst landscape defined by sinkholes, springs, and solutionally enlarged voids. Water once rushed through this area underground. Now, it lingers, rising just enough to fill the cavern’s base. The resulting habitat, both wet and stable in temperature, became an ideal roosting site for a highly specialized species: Myotis grisescens, the Grey Bat.
Why the Grey Bats Choose This Place
Grey Bats are federally endangered and extremely picky about where they roost. Unlike many bat species that scatter themselves in small groups across a range of caves, Grey Bats congregate in large numbers. Within Nickajack Bat Cave, those numbers soar to a hundred thousand, or more.
Grey Bats require deep, warm, humid environments for summer maternity colonies, and Nickajack Cave fits the bill perfectly. The constant temperature, access to water, and minimal human disturbance allow female bats to raise their pups in relative safety. In the evenings, they emerge en masse to feed on insects. Their diets consist mostly of moths, beetles, and aquatic insects. These grey bats often fly 20 miles or more in a single night.
Because the cave is now partially submerged, humans are effectively fenced out, both physically and legally. A protective gate at the cave mouth keeps visitors from disturbing this critical roosting site. From my kayak, I could drift just close enough to feel the boundary and to witness the miracle.
Twilight Emergence
As the sun melted into the hills beyond the lake, the first bats began to stir. At first it was subtle, like ripples in the air. Then suddenly, they poured from the cave mouth. Thousands of bats, forming a thick black ribbon against the orange-pink sky. Occasionally, a subtle hint of a bat wing flapping became audible, but I was untouched by the countless thousand bats fluttering all around.
I found the best vantage point a few hundred yards out, facing west. From there, the emergence silhouetted against the fading light, a perfect stage for biology in action.
This wasn’t just a tourist moment. It was the continuation of an ancient rhythm, one that predates highways and Hondas, dams and docks. These bats have likely used this cave for millennia, long before the water rose, long before the TVA drew its grid of progress across the Tennessee River Valley.
Paddling Back Through the Dark
When the light finally faded, I dipped my paddle into the dark water and glided back to the dock. I racked my boat, cinched it tight, and climbed into the Hondaminium. With the windows down and a touch of river air still clinging to me, I drove off into the night.
Nickajack reminded me that science isn’t always a textbook or a lab. It’s often a living system playing out in real time. You just have to know where to look. And sometimes, you have to bring a kayak.
Take the Clyde Outside Nickajack Bat Cave Quiz to see how much you know about this ecologic wonderland.
References:
https://www.tva.com/about-tva/our-history/built-for-the-people/the-great-replacement#:~:text=Nickajack%20Dam%20is%20located%20in,%2DGeorgia%2DTennessee%20State%20lines.&text=Construction%20of%20Nickajack%20Dam%20began,line%20on%20February%2020%2C%201968
https://repository.si.edu/server/api/core/bitstreams/c119ad5c-890d-41e7-9d1a-fcd54da2618c/content
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