Nature delves into the surprising intricacies of bat language:
Bats are noisy creatures, especially in their crowded caves, where they make calls to their neighbours. “If you go into a fruit-bat cave, you hear a cacophony,” says Yossi Yovel, a neuroecologist at Tel Aviv University in Israel who led the study.
Until now, it has been difficult to separate this noise into distinct sounds, or to determine what prompted the individual to make a particular call.
To find out what bats are talking about, Yovel and his colleagues monitored 22 captive Egyptian fruit bats (Rousettus aegyptiacus) around the clock for 75 days. They modified a voice-recognition program to analyse approximately 15,000 vocalizations collected during this time. The program was able to tie specific sounds to different social interactions captured by video, such as when two bats fought over food.
Using this tool, the researchers were able to classify more than 60% of the bats’ sounds into four contexts: squabbling over food, jostling over position in their sleeping cluster, protesting over mating attempts and arguing when perched in close proximity to each other.
The algorithm allowed researchers to identify which bat was making the sound more than 70% of the time, as well as which bat was being addressed about half the time. The team found that the animals made slightly different sounds when communicating with different individuals. This was especially true when a bat addressed another of the opposite sex — perhaps in a similar way, the authors say, to when humans use different tones of voice for different listeners. Only a few other species, such as dolphins and some monkeys, are known to specifically address other individuals rather than to broadcast generalized sounds, such as alarm calls.
The bats seemed to be particularly vocal when annoyed with other bats.