Holy Bat Chat, Batgirl! Medic Is Cracking Bat Code

Bijal P. Trivedi
National Geographic Channel
January 16, 2004
Barbara French is the real Batgirl. Over the past decade French has
shared her house with a colony of up to 75 Mexican free-tailed bats
(Tadarida brasiliensis).

By watching and listening, day and night, she has decoded a basic repertoire of bat calls and deciphered the social context in which they are used. Her collection is the largest captive insectivorous bat colony in the United States and is proving to be an incredible resource for bat researchers.

French's obsession with bats began with a move to Austin, Texas, in 1981.

Texas hosts both the largest urban, and wild, bat colonies in the world. One and a half million Mexican free-tailed bats roost under the Congress Avenue Bridge in downtown Austin. Bracken Cave, near San Antonio, is the largest aggregation of mammals in the world—20 million bats gather here to give birth and raise their young.

A visit to the bridge in 1991 triggered French's fascination. "I was standing under the bridge and couldn't see a single bat, then all of a sudden a huge cloud just dropped from the underside of the bridge and flew out—I was captivated," said French, currently the science and conservation information specialist at Bat Conservation International, in Austin.

Her role as bat medic arose serendipitously after she found an injured bat near the bridge. After inquiring which animal shelter could help the creature she discovered few people cared for bats; she began treating the animals herself.

Birth of a Bat Colony

"Barbara is exceptional—she is at the extreme end of enthusiast and has done things with bats that no one can do," said Gary McCracken, a biologist at the University of Tennessee in Knoxville, who studied interactions between mother and pup Mexican free-tailed bats in the wild. "She has taken bats splattered on trucks, nursed them back to health, and performed C-sections and amputations on these animals."

Over the years many bats recovered from their injuries and were released, but some could not regain flight capacity. Gradually, these grounded bats formed a captive colony that occupied a room in French's house for more than eight years.

Little did she anticipate that caring for the bats would become another full-time job. After returning from work every day she spends up to eight hours tending to her colony: feeding, cleaning, and laundering the bats' "sleeping bags."

Mexican free-tailed bats are picky animals and difficult to keep in captivity. Their mouths are designed to catch insects in flight not to pick them out of a dish. Because many of the injured animals can no longer fly, French hand feeds the bats homemade "bug shakes"—blends of mealworms, human baby food, and vitamins—through a syringe.

"She has a great talent for working with the bats and maintaining a captive colony which is not easy—that takes a tremendous amount of time and loving care, which professors often don't have," said Brock Fenton, a behavioral zoologist at York University in Toronto, Canada, who specializes in bat vocalization and Mexican free-tailed bat communication away from the roost.

Eavesdropping on Bat Chat

As the colony grew larger French gave the bats their own turf. The "Bat Barn" is a tiny red shed that sits beside French's house, in the countryside just southeast of Austin. Inside are wooden cages carpeted with specially made denim fabric pouches which simulate the cozy roosting crevices inside caves that bats prefer.

French even installed a baby monitor in the bat barn so that she could listen to the bats chat as she fell asleep—sounds of a mother calling her baby, territorial and courtship calls.

The consequence of this intensive care is that French has handled individual bats for years and learned a portion of their diverse language which falls within the range of human hearing. "The territorial calls produced by the males are short buzzes, trills, chirps and combinations of clicks," said French as she demonstrated.

To date she has identified about 24 distinct calls and the social situations in which they are used within her bat colony.

Captivity provides a rare opportunity for detailed recordings of vocalizations at the roost, which would not be possible in a wild situation—with thousands of animals, unknown social relationships, and a cacophony of calls and bat-to-bat conversations.

"Barbara has animals that she knows intimately," said McCracken. "She knows who's who, who's the mother of whom, who are the siblings, and the history of past matings. She knows the social history of the colony and has the background to interpret the calls."

Same Words, Different Meaning?

French, with her keen powers of observation, has teamed up with George Pollak, a neurophysiologist at the University of Texas at Austin, who is using sophisticated equipment to record the bat calls. The recording equipment is particularly important because only parts of the calls are audible, or sonic; the rest is ultrasonic.

The bat sounds are complicated, almost like birdsong, said Pollak. French believes the animals are using sounds with syntax. To test the hypothesis French, Pollak, and one of his graduate students are cataloging all the calls, and analyzing the acoustic structure of each, to study how sounds are manipulated to produce different meanings.

During mating season, for example, males produce a "territorial announcement buzz" to woo females. The same sound, albeit at a different intensity and pace, seems to be used to ward off competing males. "It's the difference between saying something sweetly, and screaming those same words—they could have very different meanings," said French.

The Jane Goodall of the Bat World

Bats are incredibly social animals. They live in huge colonies and talk with one another. Pollak is interested in how the brain processes and interprets these communications. Bats are particularly good research subjects for him because they are mammals and their auditory system is enlarged, due to the importance these creatures place on hearing.

"I'm stunned when I watch her [French] in action," said Pollak. "She has knowledge of these bats, and empathy for these creatures like Jane Goodall has for her chimps. These animals are her family—she knows their faces, temperament, age, genealogy, and she recognizes their sounds."

Pollak is just one of the scientists with whom French is collaborating. Her home has become a veritable research hub with graduate students and scientists visiting and working in her barn.

"Barbara has all the talent with the animals, and she teams up with the scientists who have experience and the equipment," said Fenton, co-author of Bats. "There is always a place in science for people like her."

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