Other voices: Gestural communication of wild Bonnet Macaques Macaca radiata in the Bandipur National Park, Southern India

Gupta, Shreejata (2016) Other voices: Gestural communication of wild Bonnet Macaques Macaca radiata in the Bandipur National Park, Southern India. Doctoral thesis, NIAS.

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Thesis advisorSinha, AnindyaUNSPECIFIED
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    Abstract: Gestural communication in nonhuman primates (henceforth, primates) has been suggested to lie at the roots of human language, perhaps the most complex form of behaviour one encounters in the living world. Comparative studies, aimed at understanding shared features of language production and usage in phylogenetically related primate species, have revealed striking similarities in characteristics between primate gestures and human language, though with certain crucial dissimilarities. Gestures in apes, for instance, are used flexibly and intentionally, and develop ontogenetically during an individual’s lifetime, traits that typify human language. Gestures produced by wild apes, nevertheless, have rarely been reported to be referential, iconic or symbolic in nature, features that are hallmarks of human communication systems. The understanding of gestural communication in our closest living phylogenetic kin is mostly derived from apes while other non-ape primate species have been largely ignored in this context. Earlier attempts to investigate gestures in a few monkey species revealed the use of flexible and intentional gestures in captivity but again, such studies have rarely been conducted in the wild. Moreover, previous research on monkey gestures had not implemented the definitions and methods standardised in ape gestural research. Thus, it has not been possible to achieve a common understanding of gestural communication in apes and non-apes, which, in turn, is indispensible for comparative and evolutionary studies. In my doctoral dissertation, I intended to address some of these unexplored areas in monkey gesture research, which would eventually contribute to a fundamental understanding of primate gestures across taxa. I conducted my investigations in the Bandipur National Park in the state of Karnataka in southern India and attempted to explore the gestural communication system of bonnet macaques, an Old World cercopithecine primate endemic to peninsular India. Several free-ranging troops of the study species, particularly in the Bandipur population, have been continuously monitored over the past two decades, revealing the presence of extensive behavioural flexibility across individual members of these groups. Such characteristic lability in behavioural expression, displayed by this population of bonnet macaques, made it highly suitable for a potential inquiry into their communication systems, especially that of gestures. The first step towards an understanding of gestures in wild bonnet macaques necessitated, as outlined above, objective definitions of the gestural signals, adopted from the ape gesture literature. I followed the various criteria of flexibility and intentionality, postulated to distinguish gestures from other communicative signals during my study. The results of such an exercise revealed that bonnet macaques do indeed produce flexible and intentional gestures, manifest in the use of multiple gestures in a single context or a single gesture in multiple contexts and as persistent gesturing in the absence of an appropriate response from the audience until the signaller’s goals were achieved. My observations also indicated that some of the gestures might have been used by the macaques in a potentially referential, intentional manner, a hypothesis that demands further exploration in the future. In addition to the gestural repertoire of the study species, I also determined the functional meanings of each gesture, as revealed by the appropriateness of the recipient’s responses, aiding the signaller to achieve its original intended goal. Most of the gestures could be classified into distinct contextual categories, with the exception of a few, which were ubiquitously used across all several contexts, perhaps indicating their inherent flexibility. In order to further characterise the gestural repertoire of the macaques, I compared the age- and sex-specific gestural repertoires across my study individuals. There appeared to be significant differences in the repertoire sizes of individuals across age classes, with the affiliative and agonistic gestural repertoires significantly increasing and the play repertoire decreasing with progressing age. These results were indicative of gradual developmental processes leading to the ultimate adult repertoire in the species. Moreover, each study troop had distinct patterns of gestural repertoires across age classes, suggesting the influence of immediate socio-ecological factors in shaping the final gestural repertoire of the study troops. There was also a distinct variability in the repertoire sizes of adult females and males, with affiliative gestures being significantly more represented in the female repertoire than in that of the males. This perhaps reflects the variable social roles that members of each sex have been independently selected for during the evolution of the species. There were no significant influences of an individual’s social rank in the dominance hierarchy on the size of their gestural repertoires. Individual repertoire sizes did not vary significantly within an age-sex class and no idiosyncratic gestures could be identified in any subject, evoking the possibility of processes other than ontogenetic ritualisation to underlie the development of bonnet macaque gestural communication. Finally, there were several gestures that were used in a single context as well as single gestures deployed across contexts, confirming the flexible nature of gesture use by the study bonnet macaques. Similar analyses of age- and sex-based differences in the frequencies of gesture use revealed that juveniles displayed the highest frequencies of gestures across contexts. Affiliative gesturing was employed comparably across different age classes, agonistic gestures were used at relatively higher frequencies by adults while play gestures were more frequent among juveniles and infants. Amongst adult females and males, affiliative and agonistic gesturing were both higher in the females, possibly reflective of a typically female-bonded primate society. Play gestures, in contrast, were exhibited more by males, possibly due to the presence of subadults, these levels significantly decreasing with increasing age of the males. Gesture frequencies also varied amongst the age classes across the study troops, which could be attributed to their immediate social environments rather than their corresponding repertoire size. Affiliative gesturing was observed to be highest among adult female-infant pairs and adult female-female pairs, perhaps emerging from the close association of these two classes of individuals. Juveniles and infants appeared to direct play gestures significantly more towards members of their own age cohorts rather than towards one another. The social dominance ranks of signallers and recipients did not influence levels of affiliative gesturing within adult females or within adult males. Agonistic gestures, however, were more significantly directed down the dominance hierarchy in both sexes of the study macaques. Rank differences between adult individuals also did not affect the frequencies of gesturing towards one another in same-sex pairs. When the gestural profiles of infant and juvenile bonnet macaques were closely examined, I observed the frequencies of tactile gesture use to be comparable across all individuals while there was a gradual development of visual gestures from young infants to the older juveniles. Agonistic gestural repertoire size and the frequencies of use of such gestures were found to be significantly higher in older juveniles whereas affiliative and play gestures were comparable across these age categories. I then investigated the influence of certain innate factors such as individual age and repertoire size as well as certain social factors such as the mother’s social rank and frequencies of received contextual gestures on the processes underlying the development of gestures across my study infants and juveniles. Generalised linear modelling of these factors and their combinations indicated repertoire size and progressive age to significantly influence gesture use, particularly in the context of agonism. The levels of display of play gestures, in contrast, depended directly on the frequency of similar gestures received, indicating the importance of the surrounding social environment in the expression of such gesturing. These results indicate that processes other than ontogenetic ritualisation, which has been postulated to underlie the appearance of ape gestures, may be responsible for the development of gesturing in this macaque species. Finally, my study on bonnet macaques revealed the use of gesture sequences—gestures combined with other gestures or other signals—by individual subjects during their communicative acts. I investigated such sequences to unravel their conventional structures, if any, through Markov transition analyses and also attempted to understand the possible meanings of such sequences. My analyses revealed significant structural components in such sequences, with certain gestures invariably used either at the beginning or at the end of a particular sequence, with the former perhaps fulfilling the function of attracting the attention of target recipients. Certain gestures also had significantly higher probabilities of being associated with other particular gestures or signals, resulting in independent communicative networks constituted by affiliative-play or agonistic gestures. Although the functional meaning of such gesture sequences were not very apparent in every situation they were used in, they seemed to be significantly more effective in eliciting responses from targetted recipients, than were the same gestures repeatedly performed singly or other, functionally similar, single gestures, during persistent gesturing by signallers following an initial failure to evoke an appropriate response. What is clear, however, is that these gesture sequences, though an intrinsic component of the communication repertoire of bonnet macaques, do not appear to be functionally similar to the syntax of human language; their presence in the gestural repertoire of the species, nonetheless, should motivate us to design further studies in order to precisely determine their functions in the communication system of this macaque. In conclusion, my research is probably the first of its kind to explore the gestural communication of any non-ape species in its natural environment, systematically employing the standardised protocols of gesture research established in ape communication studies. This, I hope, will be a fundamental contribution to the scholarship of primate communication studies and in the process, open up exciting avenues in our endeavour to understand the evolution of primate gesturing, in general and the origins of human language, in particular.
    Item Type: Thesis (Doctoral)
    Additional Information: The thesis was submitted to Manipal University, Manipal. [Year of Award 2016] [Thesis No. TH25]
    Subjects: School of Natural and Engineering Sciences > Animal Behaviour
    Programmes > Ecology, Behaviour and Conservation
    Divisions: Schools > Natural Sciences and Engineering
    Depositing User: K Rajesh
    Date Deposited: 03 May 2016 10:40
    Last Modified: 10 Jul 2017 10:10
    URI: http://eprints.nias.res.in/id/eprint/1067

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