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      Bonobos Extract Meaning from Call Sequences

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      PLoS ONE
      Public Library of Science

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          Abstract

          Studies on language-trained bonobos have revealed their remarkable abilities in representational and communication tasks. Surprisingly, however, corresponding research into their natural communication has largely been neglected. We address this issue with a first playback study on the natural vocal behaviour of bonobos. Bonobos produce five acoustically distinct call types when finding food, which they regularly mix together into longer call sequences. We found that individual call types were relatively poor indicators of food quality, while context specificity was much greater at the call sequence level. We therefore investigated whether receivers could extract meaning about the quality of food encountered by the caller by integrating across different call sequences. We first trained four captive individuals to find two types of foods, kiwi (preferred) and apples (less preferred) at two different locations. We then conducted naturalistic playback experiments during which we broadcasted sequences of four calls, originally produced by a familiar individual responding to either kiwi or apples. All sequences contained the same number of calls but varied in the composition of call types. Following playbacks, we found that subjects devoted significantly more search effort to the field indicated by the call sequence. Rather than attending to individual calls, bonobos attended to the entire sequences to make inferences about the food encountered by a caller. These results provide the first empirical evidence that bonobos are able to extract information about external events by attending to vocal sequences of other individuals and highlight the importance of call combinations in their natural communication system.

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          Most cited references83

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          The acoustic structure of suricates' alarm calls varies with predator type and the level of response urgency.

          The variation in the acoustic structure of alarm calls appears to convey information about the level of response urgency in some species, while in others it seems to denote the type of predator. While theoretical models and studies on species with functionally referential calls have emphasized that any animal signal considered to have an external referent also includes motivational content, to our knowledge, no empirical study has been able to show this. In this paper, I present an example of a graded alarm call system that combines referential information and also information on the level of urgency. Acoustically different alarm calls in the social mongoose Suricata suricatta are given in response to different predator types, but their call structure also varies depending on the level of urgency. Low urgency calls tend to be harmonic across all predator types, while high urgency calls are noisier. There was less evidence for consistency in the acoustic parameters assigned to particular predator types across different levels of urgency. This suggests that, while suricates convey information about the level of urgency along a general rule, the referential information about each category of predator type is not encoded in an obvious way.
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            Language evolution: semantic combinations in primate calls.

            Syntax sets human language apart from other natural communication systems, although its evolutionary origins are obscure. Here we show that free-ranging putty-nosed monkeys combine two vocalizations into different call sequences that are linked to specific external events, such as the presence of a predator and the imminent movement of the group. Our findings indicate that non-human primates can combine calls into higher-order sequences that have a particular meaning.
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              Campbell's monkeys concatenate vocalizations into context-specific call sequences.

              Primate vocal behavior is often considered irrelevant in modeling human language evolution, mainly because of the caller's limited vocal control and apparent lack of intentional signaling. Here, we present the results of a long-term study on Campbell's monkeys, which has revealed an unrivaled degree of vocal complexity. Adult males produced six different loud call types, which they combined into various sequences in highly context-specific ways. We found stereotyped sequences that were strongly associated with cohesion and travel, falling trees, neighboring groups, nonpredatory animals, unspecific predatory threat, and specific predator classes. Within the responses to predators, we found that crowned eagles triggered four and leopards three different sequences, depending on how the caller learned about their presence. Callers followed a number of principles when concatenating sequences, such as nonrandom transition probabilities of call types, addition of specific calls into an existing sequence to form a different one, or recombination of two sequences to form a third one. We conclude that these primates have overcome some of the constraints of limited vocal control by combinatorial organization. As the different sequences were so tightly linked to specific external events, the Campbell's monkey call system may be the most complex example of 'proto-syntax' in animal communication known to date.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2011
                27 April 2011
                : 6
                : 4
                : e18786
                Affiliations
                [1 ]School of Psychology, University of St Andrews, St Andrews, Scotland, United Kingdom
                [2 ]Twycross Zoo, Twycross, Atherstone, United Kingdom
                University of Rennes 1, France
                Author notes

                Conceived and designed the experiments: KZ ZC. Performed the experiments: ZC. Analyzed the data: ZC. Contributed reagents/materials/analysis tools: KZ. Wrote the paper: KZ ZC.

                Article
                PONE-D-10-01366
                10.1371/journal.pone.0018786
                3083404
                21556149
                fbdf2627-7018-4853-8e2d-3f60d5973bf2
                Clay, Zuberbühler. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                : 20 August 2010
                : 18 March 2011
                Page count
                Pages: 10
                Categories
                Research Article
                Biology
                Evolutionary Biology
                Animal Behavior
                Neuroscience
                Animal Cognition
                Zoology
                Animal Behavior
                Mammalogy
                Social and Behavioral Sciences
                Anthropology
                Linguistic Anthropology
                Communications
                Semantics
                Sign Systems
                Linguistics
                Semantics
                Psychology
                Behavior

                Uncategorized
                Uncategorized

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