We therefore adopted a machine-learning approach, which proved effective in recognizing human speakers 39, and used it to evaluate the information potential of the spectral composition of these vocalizations. 1, note how aggressive calls emitted in different contexts seem and sound similar). Such an approach however, was impossible with our data ( Fig. Moreover, in many bioacoustics studies, different calls are a-priori separated into categories by human-discernible acoustic features e.g. These kinds of interactions, which are extremely common in social animals, are often grouped into a single “agonistic” behavioral category in bioacoustics studies. Indeed, nearly all of the communication calls of the Egyptian fruit bat in the roost are emitted during aggressive pairwise interactions, involving squabbling over food or perching locations and protesting against mating attempts ( Supplementary Videos S1, S2, S3, S4). One might expect most social interactions in a tightly packed group, such as a fruit bat colony, to be aggressive. Importantly, our dataset covers the complete repertoire used by these bats over a period of 2.5 months, as we continuously recorded the vocalizations of the bats and their behavior. Over the course of 75 days, we recorded tens of thousands of vocalizations, for many of which (~15,000) we were able to determine both the behavioral context as well as the identities of the emitter and the addressee. We housed groups of bats in acoustically isolated chambers and continuously monitored them with video cameras and microphones around-the-clock. Egyptian fruit bats are social mammals, that aggregate in groups of dozens to thousands of individuals, can live to the age of at least 25 years 35, and are capable of vocal learning 36. In this study, we used the extremely social and vocal Egyptian fruit bat ( Rousettus aegyptiacus) to elucidate some of the huge potential of information capacity in a mammalian vocal communication system. They rely heavily on vocalizations for social communication 14, 27, 34, yet little is known about the function and informational content of these vocalizations. Other studies have exemplified the ability to distinguish between emitting individuals based on acoustic features of their vocalizations 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, while several studies, mainly in primates, revealed subtle context-dependent acoustic modifications of calls in everyday behaviors, such as food-related behaviors 32, agonistic interactions 33, and long-distance calls 29.īats are social mammals that often roost in very large colonies, and commonly engage in social interactions. Notably, the distinctive alarm calls of some species are acoustically unique to different types of danger 17, 18, 19. For example, many studies indicated the existence of context specific vocalizations in various taxa (e.g., birds 8, 9, 10, cetaceans 11, 12, dogs 13, bats 14, 15, and nonhuman primates 16). Identifying context specific calls can be a first step toward the recovering of meaning in animal communication. Thus, the information capacity of animal vocalizations should still be explored, even when interpreting the behavioral responses is not straightforward 7. Many vocalizations evoke a response according to their context or their receiver’s internal state 6, and not solely based on their acoustics. However, the requisite for a specific response might be too strict, ignoring many other information bearing vocalizations. signals which are both specific to a certain context and elicit an appropriate response by a receiver 3, 4, 5. Indeed, several studies have described cases of vocalizations as functionally referential, i.e. Researchers of animal communication, seeking homology to semantics, may relate behavioral observations to acoustic measurements, and thus reveal some of the information content of vocal expressions. Yet, in the research of nonhuman animals, the purpose and meaning of the vocal message often remain obscure. Understanding the encapsulated information in animal vocalizations is central to the study of sociality, communication, and language evolution. Many animal species use vocal communication 1, but the chaotic nature of the acoustics of these vocalizations often complicates their cataloging into clearly divided types and contexts 2.
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