We all know how difficult parties can be for making sure you are heard by the person you want to reach, and not by everyone else. Some people do it better than others. None of us, however, manage it as well as Egyptian fruit bats (Rousettus aegyptiacus), who have evolved ways to communicate effectively while surrounded by thousands of others, all trying to have their say.
Like other bat species, Egyptian fruit bats roost in large colonies, making it difficult for individuals to make sure their message reaches its target, whether it is an invitation for sex or battle.
Dr Yossi Yovel of Tel Aviv University studied nearly 15,000 vocalizations from 22 bats in such a roosting environment over 75 days. In a paper published in Scientific Reports, Yovel reveals that the bats’ calls not only identify who is calling, but who is being addressed and the context in which the call is happening.
Yovel held his bats in a sound-proofed chamber and monitored them 24/7 using both microphones and video cameras. Every call was recorded. To the human ear most sounded similar, but acoustic analysis revealed subtle patterns that could be matched to particular bats with an accuracy of 71 percent. He considers it likely that the other members of the colony could also recognize the source of a call at least this consistently.
More remarkably, Yovel could also work out in 50 percent of cases which bat the call was directed at. Fifty percent may not sound that good, but it is much better than chance, given the number of bats in the colony who might have been the intended recipient. One of the easier aspects to decipher was that calls directed at males and females were distinctively different, but even beyond this, there were often aspects to the call that suggested it was to a particular female bat. It was harder for Yovel to identify intended male recipients, but the bats may well have been able to do better than humans who hadn’t spent millions of years evolving the skills.
Sadly, like many families thrown together at Christmas, most of the bats’ calls were part of aggressive interactions between two bats fighting over food, perching locations, or unwelcome mating attempts. Each of these had recognizable features that allowed Yovel to determine the source of the conflict before confirming using the video.
Perhaps most remarkably, Yovel was able to use the calls to predict, albeit with only 62 percent accuracy, whether the call would lead to one bat vacating the area, or to ongoing conflict. Where one bat left, the sound alone gave an indication of whether it was more likely to be the caller or the target.
If only human messages were so clear.