Would you believe that there is a single cave in Texas where there are twice as many bats as there are people in New York City? Every night starting in March and until they migrate south for the winter, about 20 million Mexican free-tailed bats (Tadarida brasiliensis) emerge from Bracken Cave— home to the largest bat colony in the world. The bats fly out of the cave and take to the skies in a swirling vortex to prey on insects.
Kelly Sweet joined a National Geographic film crew at the cave near San Antonio, Texas, to film this feeding frenzy. Sweet was lying on the ground right in front of the cave entrance so the bats wouldn’t crash into her. “Once millions of bats are coming out, they’re flooding out so there’s not open space in the cave. You could not safely stand there because they will fly into you and get stuck in your hair.”
The bats leave the cave to consume massive amounts of moths and other insects—nursing mother bats will eat their body weight in insects every night. And there’s a whole ecosystem that depends on these bats as a food source; many of the baby bats won’t survive after they emerge from the cave. Sweet says, “A lot of the young bats were leaving the cave for the first time and there’s a flight pattern to what these bats need to do. These young bats have to leap off, have their first flight and then they need to continue to fly and they need to make it out without running into other bats or losing their way.”
A 50% Mortality Rate
A lot of things can go wrong, Sweet says. “They can die from falling from flight, they can die from being stuck in cactus, they can die from being picked up by a raptor … you have things in the air and on land that are waiting to eat the bats that can’t fly as well.” While Sweet was lying by the cave entrance, Western coachwhip snakes were slithering over her legs and around her trying to eat fallen bats. “[The snakes] were so concentrated on these morsels of food literally falling from the sky that they didn’t care less about me. I was something to crawl over or around to get to the food that was waiting for them.” Sometimes the snakes fight over the bats or pluck the ones that are stuck in the cactus barbs like fruit from a tree.
This was not exactly a comfortable field assignment, but Sweet was thrilled to be right in the action despite snakes, 100°F degree temperatures, and bat guano raining down from the sky. Sweet says, “If you really want to see into the animal’s lives, you have to go into the animal’s world. Having the privilege and being able to go and just experience and document what they’re doing is amazing.”
For Your Bucket List
Bracken Cave is managed by Bat Conservation International and is now open to the public on a limited number of nights.
Be sure to check out the rest of the Expedition Raw video series.