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A Mexican freetail bat hangs Wednesday in Professor Michael Smotherman's bat research lab's soundproof room. The lab is home to 75 bats caught at Kyle Field, says zoology graduate student Christine Schwartz.

Soaring serenade

Researchers study bat songs to learn about human speech

By: Jessica Henning

Posted: 10/25/07

Researchers at Texas A&M are studying the echolocation patterns of Mexican freetail bats to aide in the management of human speech.

Biology professor Michael Smotherman has been researching how the syllables of bats are organized in their brains and how that relates to human communication. Smotherman said the Mexican freetail bat species emit 10 to 20 pulses of sound a second, which is unique among bats in the region.

"[Bats] use their echoes to navigate and also to detect and find prey," Smotherman said.

"They have to adjust their voice for different environments or for different tasks, so they use different sounds for catching a bug, than they would for navigating through a field."

At the beginning of the project, the researchers studied the echo vocalizations of the bats inside and outside.

Smotherman said it is sometimes difficult working with the bats because the team had no reference point as to how they behave and what they want.

"It took us about two years to get to the point where we knew enough about the animals' behavior to reliably get singing and to be able to study it in a reliable way," he said.

"In the spring, we started hearing these funny noises coming out of our bats, and it turns out they were singing these songs. We had a bat downstairs that was singing the same song over and over and over."

Male Mexican freetail bats use the singing technique to attract females.

"What's exciting about the song, is that it's composed of several different syllables. It's not that different from a bird's song," Smotherman said.

He said birds put together syllables and then repeat them. But other than the Mexican freetail bats, no other mammal, except humans, creates a more complex collaboration of syllables.

The lab, located in the Biological Sciences Building, houses approximately 75 bats, most of which are males.

Smotherman said one of the experiments they have conducted involves introducing a female bat into a room and playing a song from a roost to see how long it takes her to move towards the sound source.

Smotherman said tropical bats use songs to communicate, but Mexican freetails are extremely socialized creatures because their migration patterns force them to forage in different environments.

"Other than humans, this is the only animal that listens to itself and cares about the sound of its voice," he said.

Researchers conducted a statistical analysis to make sure that the syllables create a pattern and found that each male is not singing the same song.

"Each one is singing a slightly different version of the song," Smotherman said. "[The bats] have something special in their brain that organizes the syllables. This would be something analogous to the part of our brain which controls the speech and language."

"If we can identify this region of the brain in the bat, then we will be able to explore these questions of how the brain organizes syllables and how the brain decides which syllables go together to make a meaningful sequence."