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KNOXVILLE — Thousands of bats emerge from a Texas cave famed for its enormous bat colony, all navigating with the same tool: their sonar skill to “see” with sound waves reflecting off objects around them.

What has puzzled scientists, though, is how the bats manage to successfully find their prey in the midst of thousands of other bats all using the same sonic tools, effectively jamming each other.

New research by University of Tennessee ecology and evolutionary biology graduate student Erin Gillam found that the bats beat this jamming by shifting the frequency of their calls, known as echolocation.

Gillam’s research shows that the bats, in this case a species known as Brazilian free-tailed bats, are able to send their sonar across a range of frequencies, and that when they are jammed by other bats, they can simply shift to a higher frequency.

Scientists had theorized that these shifts occurred, but had not yet shown direct evidence of it, according to Gillam.

“I think it’s a good step forward,” said Gillam. “It’s an interesting insight into how their brains work.”

This research, the first of its kind on mammals, opens new doors for potential research, including how the military might use similar techniques to avoid radar and sonar jamming.

The first step in the research was to set up speakers in the bats’ hunting area, playing recorded sonar calls tuned to a certain frequency, and analyzing how the bats responded.
As a group, the bats would shift their calls in response.

Next, Gillam took the same approach, only this time with individual bats. She found that as she shifted the recorded call, each bat would shift its call in response, maintaining a certain minimum difference with the recording.

Since the bats use the calls not only to navigate, but to locate their next meal, this ability to hear their own call becomes critical, said Gillam.

She will next turn her attention to how this ability to avoid interference works at different distances, as well as how this shift might be used to determine bats’ flight paths.

Gillam is a student of UT Professor Gary McCracken, one of the world’s leading experts in bat research, whose research encompasses the importance of bats in human culture and the preservation of various bat species.

Gillam’s research, published in the journal Proceedings of the Royal Society B, can be found online at http://www.journals.royalsoc.ac.uk/link.asp?id=475401x85m32x817

You can hear some of the bat calls Gillam recorded at http://sunsite.utk.edu/mp3/ur/Echolocation Calls 2.wav


Erin Gillam (865-974-6188, egillam@utk.edu)
Jay Mayfield (865-974-9409, jay.mayfield@tennessee.edu)