Bats: Avoiding Noise Overlap When Foraging In a Group

Individual bats use sonar calls when navigating in the dark, relying on the echo of their signature sounds to identify and target potential prey. But how are they able to recognize their own signals when traveling in a large group?

A new study from Tel Aviv University (TAU), Israel, suggests bats avoid noise overlap by increasing the volume, duration and repetition rate of their own unique signals, according to a news release.

"Imagine you are at a cocktail party where everyone is uttering the same word over and over again, and you are expected to recognize the echo of your own utterance to identify the location of the punch bowl," Dr. Yossi Yovel, one of the study researchers from TAU's Department of Zoology, said in the release.

"Now imagine that this is tantamount to your survival. This is the bat experience. Bats often fly in groups and rely on sounds -- very similar sounds -- to find their food," he added. "They deal with two challenges: They need to detect weak echoes in a cluster of noise, and if they manage to receive the echo, they need to recognize it as their own."

To test bat responses in high density situations, researchers played recorded echolocation calls from multiple speakers to jam the echoes of five flying Pipistrellus kuhlii bats. This was designed to imitate many bats flying in proximity to one another.

Under severe interference, researchers found bats emitted calls of higher intensity and longer duration, and called more often. However, contrary to previous beliefs, they did not change the pitch of their signals.

"In the current study, we trained bats to fly around a small room and land on a small object -- in the midst of a loud mixture of bat signals playing overhead. They found the object by increasing their emissions: crying louder and longer and shouting more frequently," Dr. Yovel explained. "They cried 'ahhhhhhh' instead of 'ah' twice as frequently -- every 50 milliseconds instead of the usual 100 milliseconds."

Researchers suggest their findings, recently published in the Proceedings of the Royal Society B: Biological Sciences, may be useful for developing improved military and civilian radar systems, which are vulnerable to electronic interference.

"We want to understand the problem," Dr. Yovel continued in the university's release. "The better we understand the radar interference problem, the easier it will be to solve. In the future, we will all have radar systems in our cars, and there can be hundreds of these on a stretch of highway as well. Individuality must be built into these radar codes, very clear signature codes."

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