Bracken Cave and The Largest Bat Colony in the World

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Near San Antonio, a 1,521-acre property houses the world’s largest bat colony. Welcome to Bracken Cave, where millions of Mexican free-tailed bats roost each year between March and October.

Have you ever seen a million of anything? Probably not. But each day, as the sun sets, viewers get to see an unbelievable sight as millions of bats swarm and swirl in intricate formations, like a mesmerizing ballet in the air.

In this article, you’ll learn all about Bracken Cave and the massive bat colony that calls it home.

History of Bracken Cave and Construction Controversy

Bracken Cave is roughly 30 miles northwest of San Antonio. The cave and undeveloped 1521 acres around it are owned and maintained by the Bat Conservation International in Austin. They purchased the cave back in 1991.

The cave itself, carved over thousands of years through the erosive forces of water, is made of limestone. The cool and dark interior creates an ideal environment for the fascinating creatures inside, shielding them from harsh weather conditions and predators. It is simply an optimal location for female Mexican free-tailed bats to safely give birth each year.

In recent years, there was some controversy regarding the land and the interests of a development company. They wanted to start construction of about 3500 homes near the cave, using the terrain of trees that the bats fly over. The Bat Conservation International and The Nature Conservancy felt that putting so many houses in the bats’ flight path would spell doom for the animals.

Residents would feel uncomfortable or threatened, and the bats might end up near or around the homes in great numbers. Homes would become locations to roost, swimming pools the new bar. If a child played with a bat, a rabies shot would be needed. Eventually, the innocent bats would be the villains.

There was a face-off with developers as politicians and the people of Texas fought to preserve this one-of-a-kind cave. They ultimately bought the land for a little over $20 million from Galo Properties in 2014.

A bat mother nurses its pup.

The Bat Situation at Bracken Cave

Fifteen to twenty million bats call this cave home. How do they manage?

While the males roost elsewhere in smaller groups, the females spend their winters in Mexico and Central/South America. They return to Bracken Cave after the winter, and then give birth to a pup toward the end of June. As scores of female bats repeat this process, the population nearly doubles in a single year.

These naked pups are left on the cave walls in massive groups, called creches. The temperature inside of Bracken Cave is a steamy 102-104 degrees, due to the concentration of tightly-packed bats and massive amounts of guano that serve as insulation. You might find stacks of up to 500 pups per square foot of cave space.

Hairless and pink, these pups get to focus their energy on growing and nursing, rather than regulating their own temperature. This also allows the mothers to freely leave to hunt. Twice a night, the mothers return to nurse the young.

The Gruesome Side of a Dense Population

You might be wondering how the population can sustain growth like I’ve described. The sad reality is that at least half of these babies will not make it to the next year. After just four or five weeks, the young begin to attempt flying. But these conditions are not forgiving. When there’s millions of baby bats attempting to do the same thing, collisions are common. They drop into complete darkness and attempt to somersault and return to the wall just seconds after taking off. The bats have to test their echolocation for the first time, and avoid the other baby bats or risk falling.

What’s waiting for them at the bottom of the cave floor? Millions of carnivorous dermestid beetles, which have experienced their own boom in population. These beetles thrive on the fallen pups, and reduce a poor victim to a cleaned skeleton in just a few minutes. It’s almost like jumping into a lake full of piranhas; the stakes are high to put it gently.

A human skull lays covered in dermestid beetles, which are flesh-eating beetles found inside Bracken Cave.
Dermestid beetles patrol the floors and walls inside Bracken Cave.

Types of Bats at Bracken Cave

At Bracken Cave, the Mexican free-tailed bats run the place. Their unique adaptations include distinctive long and tapered wings, and they can fly at speeds of up to 60 miles (96 km) per hour. Since they need to avoid collisions and still find enough food to survive, they have evolved to perform agile flight maneuvers, navigating through narrow passages with ease. These bats locate prey with exceptional accuracy, and evolution has enabled them to thrive specifically in this environment.

Scientists hope to take a core sample of the guano inside, and learn more about other species of bats that may have predated the Mexican free-tailed bat.

Other Animals at Bracken Cave

Along with these beetles, there’s a variety of flora and fauna to be found here. But most people are interested in the bat spectacle that takes place each evening.

Bats aren’t without natural predators, either. As the sun begins to set, snakes and hawks make their way over, along with raccoons, skunks, and great horned owls. The western coachwhip snake blends in flawlessly with the limestone around the entrance of the cave. When bats fall to the ground, stunned from a collision, the coachwhip takes advantage. Red-shouldered and Swainson’s hawks fly overhead, diving through the vortex of bats ot get

An image of the western coachwhip snake that eats bats at Bracken Cave.
The western coachwhip snake

The Incredible Bat Spectacle

The show starts with the barely audible fluttering of wings in the darkness. A few brave scouts emerge and quickly return to the cave. Then, a trickle of bats appears, which gradually turns into a stream. Like a rapid crescendo, this stream evolves into a flood, and a flurry of millions pop out of Bracken Cave.

For the next three hours, millions of free-tailed bats form a swirling bat vortex, circling at the mouth of the cave, and ultimately splitting apart in the air. You get to see mothers and the young that have figured out their own flight, darting through the night sky and capturing insects for their meals.

An animal behavior expert named Leonard Ireland studied these bats in the 1960s and 1970s. He reported that the massive clouds of bats were up to 30 miles (48 km) long and 20 miles (32 km) wide. It goes without saying that this is a show like nothing else on Earth.

A Whole Lot of Bat Poop

Bat poop is called guano. And 15 million is a lot of bats. They do an exceptional job on the insects, but all of that food has to go somewhere. In Bracken Cave, this guano ends up accumulating on the floor along with the hungry beetles. Each year, estimates of 50 tons of guano pile on top of the cave floor, and guano miners once reported that they dug down 60 feet in some places and never reached the bottom.

A pile of bat guano, similar to what is found on the floors of Bracken Cave.
Watch your step!

The Best Pest Control

An image shows a close-up of a cotton bullworth moth.
Cotton bullworth moth

Bats prey on numerous insects, including beetles, bugs, flies, moths, and cockroaches. The Mexican Free-Tailed Bat mostly eats moths, but also flies, ants, wasps, dragonflies, and beetles. In October, they collide with bugs such as cotton bollworth moths and army cut-worm moths being pushed away from crops southwest by winds.

This incredible feast, that takes place each night, erases tons of insects and saves money at the same time. Research in 2006 estimated that cotton farmers save over $1,000,000 in south central Texas per year due to this natural pest control.

At the same time, these bats contribute immensely to the pollination of local plants. It goes without saying that preserving Bracken Cave and its bat population is essential to a lot of parties in Texas Hill Country.

How to Visit and Enjoy the Spectacle

The cave is managed by Bat Conservation International (BCI), which is a non-profit organization. Therefore, it’s only accessible to the public through BCI-led tours. It’s a chance for a unique and educational experience for the whole family. However, be mindful of where you are, if you do end up visiting. Flash photography and loud noises are strictly prohibited, and there’s no tolerance for disrespect to the fragile environment here.

A Membership in Bat Conservation International starts at $45, and allows you to attend Member Nights. Be fast though, as memberships for viewing on individual days sell out quite regularly. For a public viewing, it costs $30 per person of all ages. No tickets are sold on site, and there are no refunds.

If you’d like to learn more about bats, check out this post on interesting bat facts next.

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