Bat chatter has implications for human communication

Tel Aviv University researchers analyze 15,000 calls to see which signal friend or foe.

By JUDY SIEGEL-ITZKOVICH
BATS FLY in a cave near Tel Aviv in July 2012. Israeli scientists are researching how the winged mammals communicate to help understand the evolution of human language and possibly pave the way for improved radar and robotic technologies. (photo credit: NIR ELIAS / REUTERS)
BATS FLY in a cave near Tel Aviv in July 2012. Israeli scientists are researching how the winged mammals communicate to help understand the evolution of human language and possibly pave the way for improved radar and robotic technologies.
(photo credit: NIR ELIAS / REUTERS)
Bats may seem scary to those who falsely believe that the nocturnal animals fly into people’s hair, but they are, in fact, extremely social mammals.
Living for 20 to 30 years in large colonies and relying heavily on interactions with others for survival, the flying mammals use vocalizations – or calls – for communication. But very little has been known about the purpose and content of these noises, until now.
A Tel Aviv University study recently published in Scientific Reports extracted critical information from bat vocalizations to offer a rare, informative look into how bats communicate. The research, led by Prof. Yossi Yovel of the zoology department at TAU’s Faculty of Life Sciences, looked at the veritable cacophony emitted by bats to discover evidence of a socially sophisticated species that learns communication, rather than being born with a fixed set of such skills.
“When you enter a bat cave, you hear a lot of ‘gibberish,’ a cacophony of aggressive bat noise. But is this merely ‘shouting’ or is there information amid the noise?” wondered Yovel. “Previous research presumed that most bat communication was based on screaming and shouting. We wanted to know how much information was actually conveyed. And we wanted to see if we could, in fact, extract that information.”
Mor Taub and Yosef Prat, students in Yovel’s lab, recorded sounds emitted by 22 Egyptian fruit bats in TAU’s own bat cave over the course of 75 days. The authors then assembled a dataset of approximately 15,000 vocalizations, which represented the full vocal repertoire the bats used during the experiment.
By analyzing this dataset, the researchers found that the vocalizations contained information about the identity of the bat emitting the call and the identity of the one being addressed.
While most of the species’ vocalizations were emitted during aggressive encounters, by analyzing the spectral composition of the calls, the authors were able to distinguish their specific context of the aggression, such as squabbles over food, sleeping spots or other resources.
“Studying how much information is conveyed in animal communication is important if you’re interested in the evolution of human language,” said Yovel.
“Specifically, one big unknown in the world of animal communication is their grasp on semanticity; such as when you hear the word ‘apple,’ you immediately imagine a round, red fruit. We found in our research that bat calls contain information about the identities of the caller and the addressee, which implies that there is a recognition factor. We were also able to discern the purpose and the context of the conversation as well as the possible outcome of the ‘discussion.’” Due to the difficulty of cataloging animal calls, vocalizations in acoustic studies have often been grouped into one category. The new findings suggest that delving into animal calls could serve a bigger purpose and shed light on the overall evolution of communication, according to Yovel.
“We generated a massive amount of data – dozens of calls over three months,” he continued. “We have found that bats fight over sleeping positions, mating, food, or just for the sake of fighting. To our surprise, we were able to differentiate between all of these contexts in complete darkness, and we are confident bats themselves are able to identify even more information and with greater accuracy. They are, after all, an extremely social species that live with the same neighbors for dozens of years.”
The researchers were even able to identify different intonations indicating greetings of a friend or foe. Yovel – who is currently researching different bat accents and their different social groups – said that last finding “allowed us to predict whether the two would stay together or part, whether the interaction would end well or badly.”