This is so cool!
Bats are social animals, with extremely sophisticated vocal and auditory abilities. It stands to reason that like other mammals and birds, bats communicate vocally. But understanding the vocalizations of any species requires significant samples of vocalization in a natural context.
Youef Prat, Mor Taub, and Yossi Yovel of Tel Aviv University report this month on a study which observed a colony of Egyptian fruit bats (said to be “extremely social and vocal” animals) for 75 days, collecting over 10,000 recordings with video . Bats roost in groups in dark caves, so in the absence of visual signals, their vocalizations would be expected extremely important social signals.
This study is quite a significant piece of work, and only a thorough and detailed approach like this can untangle the complexities of social communication.
“We continuously recorded the bats, and assembled a dataset that represents the full vocal repertoire which was used during the experiment period. is very large dataset of vocal interactions included a careful categorization of the context and participants, and enabled us to uncover the information embedded in everyday aggressive vocalizations.”
These data made it possible to determine “who said what to whom”, and also the context and results of the communication.
This chatter is essentially impossible for humans to understand, so the study employed digital signal processing and machine learning combined with manual annotations of the video (the context of the sounds).
The study found quite a bit of cool stuff about what these bats are talking about. Since the humans could determine the sex of the intended target (the “addressee”), and in many cases, the specific individual addressed, it seems clear that the bats themselves can recognize who is addressing who.
The content of the messages often concerned squabbles about food, mating, and personal space that frequently occur in this closely snuggled colony. Again, since the researchers could distinguish these cases, it is likely that an evesdropping bat “can potentially infer, fairly well, the context of the quarrel based on the vocalizations of the individuals involved”. I.e., the bats understand what is going on in the colony, based on the chatter.
The researchers also could determine which bat, if either, would leave. That is, from the message, they could predict the outcome of the quarrel.
It is important to note that this study doesn’t really tell us what bats really know, how the vocalizations help them survive, or how they evolved. But their study gives a strong indication of what information is encoded in these vocalizations, which is almost surely “understood” by the bats.
Logically, this is actually a baseline, suggesting the minimal information in the messages. Indeed, their analysis used only some of the acoustic features, and it is very likely that the bat’s brains use more features or different encodings.
The authors point out that their ability to distinguish the addressee of a vocalization is quite significant. This implies that bats can identify each other as individuals, which puts them into the growing club of species known to be able to do that.
Very nice work.
- Yosef Prat, Mor Taub, and Yossi Yovel, Everyday bat vocalizations contain information about emitter, addressee, context, and behavior. Scientific Reports, 6:39419, 12/22/online 2016. http://dx.doi.org/10.1038/srep39419