June 6, 2009

Bats Recognize The Calls Of One Another

A new study shows that bats use sound for more than direction.

Scientists from the University of Tuebingen, Germany and the University of Applied Sciences in Konstanz, Germany have found that bats have the ability to recognize each other using sound.

The researchers began their study by testing how well four greater mouse-eared bats could distinguish between echolocation and the calls of other individual bats.

They noted that the bats accurately identified the calls of other bats.

"Each bat was assigned two others it had to distinguish between," said Dr Yossi Yovel from the Weizmann Institute of Science, Israel. "So we trained bat A on a platform, playing a sound from bat B on one side and from bat C on the other. He had crawl to where the 'correct' sound was coming from."

If the bats made the correct choice and crawled into the direction of the bat where the correct sound was coming from, they were rewarded with a mealworm.

"Then, in the next stage - the test - we rewarded them no matter what choice they made, and they still chose correctly more than 80% of the time," said Dr Yovel.

"So we knew the bats were able to distinguish individuals. But it wasn't clear what they're using to discriminate one from the other," he told BBC News.

"If you think of this in comparison with humans, it's like being able to recognize a person just by listening to the same one-syllable yell in different voices.

"The bats learned the voice by listening to hundreds of very short 'yells', but they then were able to recognize an individual based on one single yell."

Researchers then created a computer model that would reproduce the recognition behavior of bats. Analysis of the model suggests that the spectral energy distribution in the signals contains individual-specific information that allows one bat to recognize another, they said in the journal PLoS Computational Biology.

"The model takes all the calls the bat thought were A, and all the calls it thought were B, and tries to understand what differences it is using to match them up," said Dr Yovel.

"Our analysis showed that each bat has a typical distribution in the frequencies it emits, probably a result of the differences in each animal's vocal chords."

Researchers said this explains how bats are able to recognize each other in dark caves as well as travel in groups at high speeds at night.


On the Net: