Bracken Cave Bats

by Stan Tekiela
© NatureSmart
August 30, 2009

I must have an affinity for anything that flies. Otherwise, what else would explain way I am standing in the middle of the hill country of Texas on a hot and steamy summer evening? It’s almost 7 PM and the temperature is still 101 degrees F and the humidity is ridiculously high. Just standing here the sweat is dripping down my back.

Even though you can cut the hot summer air with a knife it hasn’t rained in several months. Instead of a being surrounded by a lush green landscape, the hills, fields and road sides is every shade of brown indicating the drought. A very strange dichotomy indeed.

So what brings me to central Texas at this hot and uncomfortable time of year? Well, if you know me at all, you’re probably guessing it’s some kind of rare and interesting bird. Well, that’s close but it’s not a bird that brings me to Texas. It is a mammal—the Brazilian Free-tailed Bat or also called the Mexican Free-tailed Bat.

I’ve come to Bracken Cave, a large 600 feet long cave that is owned and protected by Bat Conservation International (BCI). It’s a highly restricted cave and I’m here at a private invite. For at least the last 10,000 years this cave has been home to millions of bats each summer.

The entrance of the cave sits at the side of a large depression in the ground. Approaching the cave from the east you can’t help but smell the characteristic odor of an active bat cave. The pungent smell floats around on the warm summer’s breeze as natural as the Fence Post lizard scrambles amongst the rocks. 

Moving around to the western side of the cave the large eyebrow shaped entrance of the cave comes in to view. Even though it is nearly 2 hours before sunset there are thousands of bats swirling around at the cave entrance. Moving in perfect concert with each other the bats fly in ever expanding circles with one half of the circle inside the cave and the other half outside the cave. Around and around they go. It’s a very impressive site and I am getting excited at the prospects of the event that is about to unfold before me.

As I set up my camera gear and flash I can see the amount of bats swirling at the cave entrance is building. The swirling mass of bats is bulging and now more than half of the flight circle is outside the cave. I can hear the flapping of all those wings. For some reason I expected there to be more noise and more ciaos but it’s very quite and very well organized.

Now the swirling mass of bats has moved completely out of the cave entrance and is gaining altitude. Like a spinning vortex the massive group of thousands of bats ascends upward filling the evening sky. At this moment I can feel the wash of air produced from all the wings beating together. The first batch of bats is now joined by many thousands more exiting the cave and joining the spinning vortex. At the apex of the swirling mass the bats stream off towards the horizon in a snaking column. The column is long and so thick it appears like a trail of smoke or a river of bats. At this moment it is a solid mass of bats emerging from the cave entrance, rising up 100 feet and trailing off and over the horizon.

There are so many bats emerging from this cave that the local Doppler Radar clearly registers the mass. There are an estimated 20 million bats in this one cave. This is the largest gather of a single mammal species on the face of the earth. All of these bats are pregnant females giving birth to a single pup. By the end of summer, presuming all the females give birth and all the young live, there could be 40 million bats in the cave. However many of the young don’t survive so it is estimated that at least 30 million bats will leave the cave at the end of summer to migrate south.

There are so many bats in the cave that the bats stream out of the cave for hours on end all evening. Each mother bat needs to go out and feed to maintain its health to be able to nurse it’s baby. Each mother bat consumes up to half it’s own body weight in insects each night for an estimated 200 tons of insects. Many of these insects are agricultural pests. It is estimated that the bats save local ranchers and farmers $1.75 million dollars in pesticide use alone.

Upon returning to the cave the bats are so tightly packed in that the ceiling of the cave has over 200 individuals per square foot. The body heat from all of these bats raises the temperature in the cave from a natural 68 degrees to over 100 degrees.

Watching the bats emerge from the cave this evening is truly an unforgettable experience. I travel the world to study, photograph and document natural history and Bracken Cave is near the top of truly wonderful places. Until next time…

 

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