By Merlin Tuttle
Inner Space Cavern, located in Georgetown, Texas, has become a bat education center thanks to cooperative tricolored bats (Perimyotis subflavus) and tour guides who love them. More than 300,000 visitors a year will have a close-up encounter with bats during their guided tour.
Tricolored bats can be seen year-round, often roosting within a few feet of passing visitors. Assistant Manager, Patty Perlaky, commented, “I think one of the most exciting things for people, especially the children, is to see a live bat in real life, not on TV.”
The cave itself has a long and fascinating history. Approximately 13,000 to 32,000 years ago it had up to five entrances, some quite large. Ancient bones and carbon dating reveal the cave was visited by saber-toothed cats, jaguars, ground sloths, spectacled bears, dire wolves, camels, and even an occasional mammoth.
It also hosted an apparent nursery colony of some 50,000 or more Brazilian free-tailed bats (Tadarida brasiliensis). The approximate number of free-tailed bats formerly using the cave can be estimated from the area covered by still conspicuous stains on the domed ceiling where they roosted.
However, about 13,000 years ago, all the cave’s entrances closed. Why remains a mystery. Layers of flowstone, deposited during the cave’s long closure, now cover free-tailed bat bones and guano on the floor.
The cave remained closed till 1963 when it was discovered accidentally by a Texas Highway Department core drilling team who found it while checking substrate firmness for an I-35 overpass.
Three years later, what is now the tour cave entry was blasted open midway between the borehole and the lowest passages. This allowed classic chimney-effect airflow with heavier winter air becoming trapped in low areas. The now cooler, but never freezing temperatures, create a safe winter hibernation site ideal for tricolored bats. They all emerge to feed periodically in spring and summer. But guides report nearly always finding at least a few that return for a cool snooze.
No one remembers when these bats first began to arrive, but they’ve always been welcome and strictly protected. Because of this unique situation, they’ve learned they’ve nothing to fear and ignore humans. Their sleep remains unperturbed despite the passage of hundreds of visitors in a single day. It’s a great place to view bats close up without causing harm.
Tricolored bats are well known for their unusual tolerance of human disturbance. However, these have learned to be especially tolerant since they are never handled or harmed. They are not the only species that has learned to ignore humans where protected. Assumptions about other species should not be made without patient and cautious testing.
No one has attempted to count these relatively recent immigrants, but they may at times approach 100. Tour guides report their numbers to be stable or increasing despite precipitous declines, due to the fungus that causes white-nose syndrome, in caves farther north.
Visitors have many questions, providing wonderful opportunities for education. Last February we hired a film crew to produce a seven-minute video for use in the cavern visitor center. Funded by MTBC member, Mindy Vescovo, it explains tricolored bats and introduces bats worldwide as sophisticated, safe, invaluable, and endlessly fascinating. It now runs continuously on large screens in the snack bar and waiting area, educating thousands of visitors weekly.
Guides showing two soundly sleeping tricolored bats to tour groups.
Historically, human use of caves has often proven disastrous for bats. However, at Inner Space Cavern, the story has been reversed, hopefully inspiring additional tour cave owners to lend a helping hand. Cavern Manager, Taunya Vessels, finds her bats to be a real asset as an added attraction.