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Many host species have evolved sophisticated defences to mitigate the high fitness costs imposed by brood parasitism. Even though the physiological mechanisms behind such defences can offer important insights into the evolutionary relationship between brood parasites and hosts, they have received little attention so fat Hormones play a critical role in the regulation of bird reproduction, which make them a key element when investigating the physiological effects of brood parasitism on hosts. Here, we experimentally parasitized Eurasian blackbird (Turdus merula) nests with non-mimetic eggs to study its impact on the hormonal levels (corticosterone and prolactin) of females during incubation, as well as the magnitude of the response to the standardized stress protocol in parasitized and non-parasitized individuals. Parasitized females had higher baseline corticosterone levels and showed a poorer body condition than non-parasitized birds, while we found no differences for prolactin levels. Both parasitized and non-parasitized females responded to the standardized-stress protocol with a significant increase in corticosterone levels. However, the decrease in prolactin after the standardized stress protocol was significantly more pronounced in parasitized individuals. Our results suggest that the presence of a non-mimetic parasitic egg involves a stressful situation for hosts, negatively affecting the physical state of parasitized females. Unaffected prolactin levels of parasitized individuals could explain the absence of nest desertion found in this species in response to parasitism. Finally, both hormones were not correlated in blackbirds, confirming that their combined study provides valuable pieces of information on the endocrine mechanisms underlying behavioural responses in animals, including hosts of brood parasites.Significance statementPhysiological mechanisms behind avian brood parasitism remain unclear. In this study, we assessed the effect of experimental parasitism on the hormonal profiles of hosts. We found that the presence of a non-mimetic egg in the nest modified baseline corticosterone levels, but not prolactin levels, of parasitized females and negatively impacted their body condition. Moreover, experimental parasitism affected the prolactin response to stress. These results expand previous information on the endocrine consequences of brood parasitism at other stages of the breeding cycle (nestling and fledgling stage) and might shed light on the hormonal mechanisms that underlie the host response against parasitic eggs.

The study was funded by a St Leonard College Inter-University scholarship awarded to JC and KZ, the Swiss National Science Foundation awarded to KZ (310030_185324), and individual grants from Swiss universities and St Leonard Santander Mobility awarded to AS. Audience effects are key in studies of animal social cognition and are typically investigated during directed social interactions. Male chimpanzees regularly perform aggressive displays in the presence of others, often targeting a specific group member, and combine this agonistic behaviour with acoustic signals. Here, we were interested in whether the production and structure of pant hoots, a long-distance signal, were influenced by audience composition (i.e., presence and absence of specific individuals). We investigated pant hoots produced during displays by adult and sub-adult males of Budongo Forest, Uganda. We found that males overall called more often when their preferred social partners and females were absent from the party, as well as when more dominant males were present. We then separately analysed the four phases of pant hoots - introduction, build-up, climax, and let-down - and found that audience composition and social context could often explain the presence or absence of each phase. In addition, displays were often accompanied by drumming, especially by older males and when male audiences were small. Our study adds to the growing body of literature on audience effects and other social factors and shows their impact on the structure of a sophisticated vocal sequence, which enhances the communicative capacity in a species with limited vocal control. Publisher PDF

This work was funded by the Swiss National Science Foundation Agreement project grants 31003A_166458 (KZ) and 310030_185324 (KZ), and the Swiss National Centre of Competence in Research (NCCR) Evolving Language, Swiss National Science Foundation Agreement #51NF40_180888 (KZ). How do animals learn to classify the world and what is the role of social learning during this process? Here, we show that young sooty mangabeys, Cercocebus atys, of Taï Forest, Côte d’Ivoire, learn to rapidly classify an unfamiliar predator by attending to others’ alarm calls and that such knowledge is retained over long periods. We experimentally exposed subjects to chimeric predator models with both snake- and leopard-like features, combined with playbacks of conspecific snake (N=12) or leopard alarms (N=13). Adults classified the chimeras as non-threatening but for juveniles, we found that one single alarm call exposure was sufficient to allocate the chimera to the snake or leopard category, suggesting plausibility judgments in experienced adults. We then retested N=10 juveniles with the same models more than a year after their first experience and found that they continued to show their original response, indicating long-term retention of socially learned predator categorisation. Publisher PDF

Funding: The study was funded by Swiss National Science Foundation awarded to KZ (310030_185324), the St Leonard College Inter-University scholarship awarded to JC and KZ, the Swiss universities cotutelle grant and the Santander Mobility Grant awarded to AS. Observations of early vocal behaviours in non-human primates (hereafter primates) are important for direct comparisons between human and primate vocal development. However, direct observations of births and perinatal behaviour in wild primates are rare, and the initial stages of behavioural ontogeny usually remain undocumented. Here, we report direct observations of the birth of a wild chimpanzee ( Pan troglodytes schweinfurthii ) in Budongo Forest, Uganda, including the behaviour of the mother and other group members. We monitored the newborn’s vocal behaviour for approximately 2 hours and recorded 70 calls. We categorised the vocalisations both qualitatively, using conventional call descriptions, and quantitatively, using cluster and discriminant acoustic analyses. We found evidence for acoustically distinct vocal units, produced both in isolation and in combination, including sequences akin to adult pant hoots, a vocal utterance regarded as the most complex vocal signal produced by this species. We concluded that chimpanzees possess the capacity to produce vocal sequences composed of different call types from birth, albeit in rudimentary forms. Our observations are in line with the idea that primate vocal repertoires are present from birth, though fine acoustic structures likely undergo ontogenetic processes. Our study provides rare and valuable empirical data on perinatal behaviours in wild primates. Publisher PDF

International audience; What factors affect imitation performance? Varying theories of imitation stress the role of experience, but few studies have explicitly tested its role in imitative learning in non-human primates. We tested several predictions regarding the role of experience, conspecific presence, and action compatibility using a stimulus-response compatibility protocol. Nineteen baboons separated into two experimental groups learned to respond by targeting on a touch screen the same stimulus as their neighbour (Compatible) or the opposite stimulus (Incompatible). They first performed the task with a conspecific demonstrator (Social phase) and then a computer demonstrator (Ghost phase). After reaching a predetermined success threshold, they were then tested in an opposite compatibility condition (i.e., Reversal learning conditions). Seven baboons performed at least two reversals during the social phase, and we found no significant difference between the compatible and incompatible conditions, although we noticed slightly faster RTs in the compatible condition that disappeared after the first reversal. During the ghost phase, monkeys showed difficulties in learning the incompatible condition, and the compatible condition RTs tended to be slower than during the social phase. Together, these results suggest that 1) there is no strong movement compatibility effect in our task, and that 2) the presence of a demonstrator plays a role in eliciting correct responses but is not essential, as has been previously shown in human studies.

This work received funding from the European Research Council under the European Union’s Seventh Framework Programme [FP7/2007–2013]/ERC grant agreement no. 283871 (PI: K. Zuberbühler), the Swiss National Science Foundation and the University of Neuchâtel, the European Research Council (ERC) under the European Union’s Seventh Framework Programme [FP/2007-2013]/ERC Grant Agreement N°324115–FRONTSEM (PI: P. Schlenker), the European Union’s Horizon 2020 research and innovation programme (grant agreement No. H2020 European Research Council 788077, Orisem, PI: P. Schlenker), from the Fyssen Foundation (post-doc grant) and from the Institut d’Études Cognitives, École Normale Supérieure − PSL Research University supported by grants ANR-10-IDEX-0001-02 and FrontCog ANR-17-EURE-0017. We acknowledge the support received from the Agence Nationale de la Recherche of the French government through the program “Investissements d’Avenir” (16-IDEX-0001 CAP 20-25); FP7 Ideas: European Research Council [283871,324115]; Fondation Fyssen; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung; Université de Neuchâtel. The emergent field of animal linguistics applies linguistics tools to animal data in order to investigate potential linguistic-like properties of their communication. One of these tools is the "Urgency Principle", a pragmatic principle stating that in an alarm sequence, calls providing information about the nature or location of a threat must come before those that do not. This theoretical principle has helped understand the alarm system of putty-nosed monkeys, but whether it is relevant for animal communication systems more generally remains to be tested. Moreover, while animal communication systems can convey information via a large set of encoding mechanisms, the Urgency Principle was developed for only one encoding mechanism, call ordering. Here, we propose to extend this principle to other encoding mechanisms and empirically test this with the alarm call system of black-fronted titi monkeys (Callicebus nigrifrons). We investigated how information about the context of emission unfolded with the emission of successive calls. Specifically, we analysed how contextual parameters influenced the gradual sequential organization of the first 50 calls in the sequence, using methods borrowed from computational linguistics and random forest algorithms. We hypothesized that, if the extended Urgency Principle reflected the sequential organization of titi monkey alarm call sequences, mechanisms encoding urgent information about the predatory situation should appear before encoding mechanisms that do not. Results supported the hypothesis that mechanisms encoding for urgent information relating to a predator event consistently appeared before mechanisms encoding for less-urgent social information. Our study suggests that the extended Urgency Principle applies more generally to animal communication, demonstrating that conceptual tools from linguistics can successfully be used to study nonhuman communication systems. Postprint

The 2008-2010 data collection was financially supported by FAPEMIG-Brazil, CAPES-Brazil, the Leakey Trust and the University of St Andrews. The 2014-2016 data collection received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement no. 283871 (PI: Zuberbühler) and the University of Neuchâtel. The 2019 research was financially supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 788077, Orisem, PI: Schlenker), from the Fyssen Foundation (post-doc grant) and from the Global Wildlife Conservation’s Primate Action Fund and the Margot Marsh Biodiversity Foundation, and the Institut d’Etudes Cognitives, Ecole Normale Supérieure - PSL Research University supported by grants ANR-10-IDEX-0001-02 and FrontCog ANR-17-EURE-0017.JCBM thanks the Brazilian National Council for Scientific and Technological Development/CNPq for a research fellowship (PQ 1C #304475/2018-1). KZ thanks the Swiss National Science Foundation 310030_185324. Platyrrhini are highly vulnerable to the yellowfever (YF) virus. From 2016 to 2018, the Atlantic Forest of southeast Brazilfaced its worst sylvatic YF outbreak in about a century, thought to have killedthousands of primates. It is essential to assess the impact of this epidemic onthreatened primate assemblages to design effective conservation strategies. Inthis study, we assessed the impact of the 2016-2018 YF outbreak on ageographically isolated population of Near Threatened black-fronted titi monkeys(Callicebus nigrifrons) in two Atlantic Forest patches ofthe Santuário do Caraça, MG, Brazil. Extensive pre-outbreak monitoring,conducted between 2008 and 2016, revealed that the home range and group sizes ofthe population remained stable. In 2016, the population size was estimated at53-57 individuals in 11-12 groups. We conducted monitoring and playback surveysin 2019 and found that the population had decreased by 68% in one forest patchand completely vanished in the other, resulting in a combined decline of 80%. Wediscuss this severe loss of a previously stable population and conclude that itwas highly likely caused by the YF outbreak. The remaining population is atrisk of disappearing completely because of its small size and geographic isolation.A systematic population surveys of C. nigrifrons, along other sensible Platyrrhini species, is needed to re-evaluate theircurrent conservation status. Postprint

Animal communication has long been thought to be subject to pressures and constraints associated with social relationships. However, our understanding of how the nature and quality of social relationships relates to the use and evolution of communication is limited by a lack of directly comparable methods across multiple levels of analysis. Here, we analysed observational data from 111 wild groups belonging to 26 non-human primate species, to test how vocal communication relates to dominance style (the strictness with which a dominance hierarchy is enforced, ranging from 'despotic' to 'tolerant'). At the individual-level, we found that dominant individuals who were more tolerant vocalized at a higher rate than their despotic counterparts. This indicates that tolerance within a relationship may place pressure on the dominant partner to communicate more during social interactions. At the species-level, however, despotic species exhibited a larger repertoire of hierarchy-related vocalizations than their tolerant counterparts. Findings suggest primate signals are used and evolve in tandem with the nature of interactions that characterize individuals' social relationships. Publisher PDF

This work has been supported by the Agence Nationale de la Recherche grant ANR-16-PILO-0002-06 as a part of FLAG-ERA joint transnational call project, FuturICT 2.0. Populist attitudes have been shown to predict voting behaviour. These attitudes consist of a belief that everyday citizens are better judges of what is best for their own country than politicians and that the political elites are corrupt. As such, a clear ‘us’ (pure and good everyday citizens) and ‘them’ (the evil political elite) rhetoric is present. In the present research, we propose that identification with the government may predict whether people would vote for, and whether they have voted in the past for, a populist party (either from the political left or the political right). The present research (N = 562), carried out among French citizens, showed that lower government identification related to past voting behaviour, current voting intentions and likelihood to switch from a non-populist to a populist party. Identification with the government was also negatively associated to intention to abstain from voting. Moreover, government identification was a stronger predictor of these voting-related outcomes than the recently developed populist attitudes measures. Unexpectedly, national identification was a not a significant predictor of voting behaviour. In conclusion, the present research suggests that the extent to which citizens identify and feel represented by the government should be considered on par with populist attitudes in understanding support for populist parties. Perceiving that the government does not represent everyday people may be sufficient to abandon support for mainstream (non-populist) political parties. Postprint

Funding: This work was supported by grants from the Agence Nationale de la Recherche (ANR-08-412 BLAN-0042-01), and the European Science Foundation (Compcog Exchange Grant n°3648). Decision outcomes in unpredictable environments may not have exact known probabilities. Yet the predictability level of outcomes matters in decisions, and animals, including humans, generally avoid ambiguous options. Managing ambiguity may be more challenging and requires stronger cognitive skills than decision-making under risk, where decisions involve known probabilities. Here we compare decision-making in capuchins, macaques, orangutans, gorillas, chimpanzees and bonobos in risky and ambiguous contexts. Subjects were shown lotteries (a tray of potential rewards, some large, some small) and could gamble a medium-sized food item to obtain one of the displayed rewards. The odds of winning and losing varied and were accessible in the risky context (all rewards were visible) or partially available in the ambiguous context (some rewards were covered). In the latter case, the level of information varied from fully ambiguous (individuals could not guess what was under the covers) to predictable (individuals could guess). None of the species avoided gambling in ambiguous lotteries and gambling rates were high if at least 2 large rewards were visible. Capuchins and bonobos ignored the covered items and gorillas and macaques took the presence of potential rewards into account, but only chimpanzees and orangutans could consistently build correct expectations about the size of the covered rewards. Chimpanzees and orangutans combined decision rules according to the number of large visible rewards and the level of predictability, a process resembling conditional probabilities assessment in humans. Despite a low sample size, this is the first evidence in non-human primates that a combination of several rules can underlie choices made in an unpredictable environment. Our finding that non-human primates can deal with the uncertainty of an outcome when exchanging one food item for another is a key element to the understanding of the evolutionary origins of economic behavior. Postprint Publisher PDF

The research was supported by a Fyssen Fellowship, British Academy Newton International Fellowship (NF171514), and CAP2025 funding awarded to G.D., funding from the European Union’s Seventh Framework Programme for research, technological development, and demonstration (Grant agreement no. 283871) awarded to KZ the Swiss National Science Foundation (PZ00P3_154741) awarded to C.D.D., the Startup-funding of Taipei Medical University (108-6402-004-112) awarded to C.D.D., and (310030_185324) awarded to KZ How did human language evolve from earlier forms of communication? One way to address this question is to compare prelinguistic human vocal behavior with nonhuman primate calls. An important finding has been that, prior to speech and from early on, human infant vocal behavior exhibits functional flexibility, or the capacity to produce sounds that are not tied to one specific function. This is reflected in human infants’ use of single categories of protophones (precursors of speech sounds) in various affective circumstances, such that a given call type can occur in and express positive, neutral, or negative affective states, depending on the occasion. Nonhuman primate vocal behavior, in contrast, is seen as comparably inflexible, with different call types tied to specific functions and sometimes to specific affective states (e.g. screams mostly occur in negative circumstances). As a first step toward addressing this claim, we examined the vocal behavior of six wild infant chimpanzees during their first year of life. We found that the most common vocal signal, grunts, occurred in a range of contexts that were deemed positive, neutral, and negative. Using automated feature extraction and supervised learning algorithms, we also found acoustic variants of grunts produced in the affective contexts, suggesting gradation within this vocal category. In contrast, the second most common call type of infant chimpanzees, the whimpers, was produced in only one affective context, in line with standard models of nonhuman primate vocal behavior. Insofar as our affective categorization reflects infants’ true affective state, our results suggest that the most common chimpanzee vocalization, the grunt is not affectively bound. Affective decoupling is a prerequisite for chimpanzee grunts (and other vocal categories) to be deemed ‘functionally flexible’. If later confirmed to be a functionally flexible vocal type, this would indicate that the evolution of this foundational vocal capability occurred before the split between the Homo and Pan lineages. Postprint

Jamais vu is a phenomenon operationalised as the opposite of déjà vu, i.e. finding subjectively unfamiliar something that we know to be familiar. We sought to document that the subjective experience of jamais vu can be produced in word alienation tasks, hypothesising that déjà vu and jamais vu are similar experiential memory phenomena. Participants repeatedly copied words until they felt “peculiar”, had completed the task, or had another reason to stop. About two-thirds of all participants (in about one-third of all trials) reported strange subjective experiences during the task. Participants reported feeling peculiar after about thirty repetitions, or one minute. We describe these experiences as jamais vu. This experimentally induced phenomenon was related to real-world experiences of unfamiliarity. Although we replicated known patterns of correlations with déjà vu (age and dissociative experiences), the same pattern was not found for our experimental analogue of jamais vu, suggesting some differences between the two phenomena. However, in daily life, those people who had déjà vu more frequently also had jamais vu more frequently. Findings are discussed with reference to the progress that has been made in déjà vu research in recent years, with a view to fast-tracking our understanding of jamais vu. Postprint

Field experiments reveal that titi monkeys probabilistically encode predator type and location using call combinations., Previous work suggested that titi monkeys Callicebus nigrifrons combine two alarm calls, the A- and B-calls, to communicate about predator type and location. To explore how listeners process these sequences, we recorded alarm call sequences of six free-ranging groups exposed to terrestrial and aerial predator models, placed on the ground or in the canopy, and used multimodel inference to assess the information encoded in the sequences. We then carried out playback experiments to identify the features used by listeners to react to the available information. Results indicated that information about predator type and location were encoded by the proportion of B-call pairs relative to all call pairs of the sequence (i.e., proportion of BB-grams). The results suggest that the meaning of the sequence is not conveyed in a categorical but probabilistic manner. We discuss the implications of these findings for current theories of animal communication and language evolution.

International audience; The concept of directed social learning predicts that social learning opportunities for an individual will depend on social dynamics, context and demonstrator identity. However, few empirical studies have examined social attention biases in animal groups. Sex-based and kinship-based biases in social learning and social attention towards females have been shown in a despotic and female philopatric primate: the vervet monkey (Chlorocebus pygerythrus). The present study examined social attention during the juvenile period. Social attention was recorded through 5-min focal observations during periods of natural foraging. Kin emerged as the most important focus of social attention in juveniles, intensified by biased spatial proximity towards matrilineal related members. The highest-ranking conspecifics were more frequently observed by juveniles than low-ranking ones. Additionally, younger and orphaned juveniles showed higher levels of social attention overall, compared to other age categories. No effect of the juvenile’s hierarchical rank was detected, suggesting that the variation in social attention recorded reflects different biases and stages of social learning and socialisation, rather than social anxiety. Juvenile females tended to exhibit a dominance-based bias more strongly than did males. This might be explained by a greater emphasis on attaining social knowledge during juvenile socialisation in the philopatric sex. Moreover, despite a preferred association between juveniles, social attention was more often directed to adults, suggesting that adults may still be more often chosen as a target of attention independent of their dominance rank.

Grant acknowledgements: Cäsar: The research leading to these results received funding from the CAPES-Brazil, FAPEMIG-Brazil, S.B. LEAKEY TRUST and the University of St Andrews. Chemla and Schlenker: Research by Schlenker and Chemla was conducted at Institut d’Etudes Cognitives, Ecole Normale Supérieure – PSL Research University. Institut d’Etudes Cognitives is supported by grants ANR-10-LABX-0087 IEC et ANR-10-IDEX-0001-02 PSL. Schlenker: The research leading to these results received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n°324115- FRONTSEM (PI:Schlenker). Zuberbühler: The research leading to these results received funding from the European Research Council under ERC grant ‘Prilang 283871’ and also from the Swiss National Science Foundation under grant ‘FN 310030_143359/1’. Cäsar et al. (2013) show that the structure of Titi monkey call sequences can, with just two call types (A and B), reflect information about predator type and predator location. Using the general methods of Schlenker et al. (2014, 2016, to appear), we ask what these observations show about the 'linguistic' structure of Titi calls. We first demonstrate that the simplest behavioral assumptions make it challenging to provide lexical specifications for A- and B-calls: B-calls rather clearly have the distribution of highly underspecified calls; but A-calls are also found in highly heterogeneous contexts (e.g. they are triggered by 'cat in the canopy' and 'raptor on the ground' situations). We discuss two possible solutions to the problem. One posits that entire sequences are endowed with meanings that are not compositionally derived from their individual parts (a related idea was proposed by Arnold and Zuberbühler to analyze pyow-hack sequences in Putty-nosed monkeys). The second solution, which we consider to be superior, takes sequences to have no structure besides concatenation: the Bcall is a general call, the A-call is used for serious non-ground threats, and each call reflects information about the environment at the time at which it is uttered. The composition of Cäsar et al.'s sequences is seen to follow from the interaction between call meaning, rules of competition among calls, and more sophisticated assumptions about the environmental context. In the end, a detailed analysis of the division of labor between semantics, pragmatics and the environmental context yields a simple and explanatory analysis of sequences that initially seemed to display a complex mapping between syntax and semantics. Postprint

Many primates produce one type of alarm call to a broad range of events, usually terrestrial predators and non-predatory situations, which raises questions about whether primate alarm calls should be considered ‘functionally referential’. A recent example is black-fronted titi monkeys, Callicebus nigrifrons, which emit sequences of B-calls to terrestrial predators or when moving towards or near the ground. In this study, we reassess the context specificity of these utterances, focussing both on their acoustic and sequential structure. We found that B-calls could be differentiated into context-specific acoustic variants (terrestrial predators vs. ground-related movements) and that call sequences to predators had a more regular sequential structure than ground-related sequences. Overall, these findings suggest that the acoustic and temporal structure of titi monkey call sequences discriminate between predator and non-predatory events, fulfilling the production criterion of functional reference. Primate terrestrial alarm calls are at the centre of an ongoing debate about meaning in animal signals. Primates regularly emit one alarm call type to ground predators but often also to various non-predatory events, raising questions about the referential nature of these signals. In this study, we report observational and experimental data from wild titi monkeys and show that terrestrial alarm calls are usually given in sequences of acoustically distinct variants composed in structurally distinct ways depending on the external event. These differences are salient and could help recipients to distinguish the nature of the call eliciting event. Since most previous studies on animal alarm calls have not checked for acoustic variants within different call classes, it may be premature to conclude that primate terrestrial calls do not meet the criteria of functional reference.

International audience; Cet article présente notre étude sur la reconnaissance vocale à long terme des partenaires sociaux chez les bonobos Pan paniscus. Ces résultats ont été publiés en 2016 dans la revue Scientific Reports 6 : 22046 | https://doi.org/10.1038/srep22046 et, avec l'accord de tous les co-auteurs, nous proposons ici une version française de cette étude pour la Revue de Primatologie. La reconnaissance sociale à long terme est vitale pour les espèces vivant dans des réseaux sociaux complexes et dans lesquels des individus familiers peuvent se rencontrer à nouveau après de longues périodes de séparation. Chez les primates non humains qui vivent dans des environnements forestiers denses, la visibilité est souvent limitée ; et, la reconnaissance des partenaires sociaux à longue distance dépend de la communication vocale. Etonnamment, la reconnaissance vocale de partenaires après des années de séparation n'a jamais été testée chez aucune espèce de grand singe, malgré l’organisation complexe de leur société et leur intelligence sociale. Nous montrons ici que les bonobos, Pan paniscus, sont capables d’une reconnaissance vocale fiable de leurs partenaires sociaux, et cela même s'ils ont été séparés pendant cinq ans. Nous avons testé expérimentalement les réponses de bonobos aux vocalisations d’anciens membres de leur groupe qui avaient été transférés entre parcs zoologiques. Malgré de longues périodes de séparation, les sujets ont répondu plus intensément aux voix familières qu'aux voix d'individus étrangers. Cette observation démontre expérimentalement que les bonobos peuvent discriminer des individus sur la seule base d’indice acoustique même des années après leur dernière rencontre. Notre étude suggère également que les bonobos peuvent cesser de faire la distinction entre des individus familiers et non familiers après une période de huit ans, indiquant que les représentations vocales ou l'intérêt pourraient être limités dans le temps chez cette espèce.

Rich data gathered in experimental primatology in the last 40 years are beginning to benefit from analytical methods used in contemporary linguistics, especially in the area of semantics and pragmatics. These methods have started to clarify five questions: (i) What morphology and syntax, if any, do monkey calls have? (ii) What is the ‘lexical meaning’ of individual calls? (iii) How are the meanings of individual calls combined? (iv) How do calls or call sequences compete with each other when several are appropriate in a given situation? (v) How did the form and meaning of calls evolve? Four case studies from this emerging field of ‘primate linguistics’ provide initial answers, pertaining to Old World monkeys (putty-nosed monkeys, Campbell’s monkeys, and colobus monkeys) and New World monkeys (black-fronted Titi monkeys). The morphology mostly involves simple calls, but in at least one case (Campbell’s -oo) one finds a root–suffix structure, possibly with a compositional semantics. The syntax is in all clear cases simple and finite-state. With respect to meaning, nearly all cases of call concatenation can be analyzed as being semantically conjunctive. But a key question concerns the division of labor between semantics, pragmatics, and the environmental context (‘world’ knowledge and context change). An apparent case of dialectal variation in the semantics (Campbell’s krak) can arguably be analyzed away if one posits sufficiently powerful mechanisms of competition among calls, akin to scalar implicatures. An apparent case of noncompositionality (putty-nosed pyow–hack sequences) can be analyzed away if one further posits a pragmatic principle of ‘urgency’. Finally, rich Titi sequences in which two calls are re-arranged in complex ways so as to reflect information about both predator identity and location are argued not to involve a complex syntax/semantics interface, but rather a fine-grained interaction between simple call meanings and the environmental context. With respect to call evolution, the remarkable preservation of call form and function over millions of years should make it possible to lay the groundwork for an evolutionary monkey linguistics, illustrated with cercopithecine booms.

Human language has evolved on a biological substrate with phylogenetic roots deep in the primate lineage. Here, we describe a functional analogy to a common morphological process in human speech, affixation, in the alarm calls of free-ranging adult Campbell's monkeys (Cercopithecus campbelli campbelli). We found that male alarm calls are composed of an acoustically variable stem, which can be followed by an acoustically invariable suffix. Using long-term observations and predator simulation experiments, we show that suffixation in this species functions to broaden the calls' meaning by transforming a highly specific eagle alarm to a general arboreal disturbance call or by transforming a highly specific leopard alarm call to a general alert call. We concluded that, when referring to specific external events, non-human primates can generate meaningful acoustic variation during call production that is functionally equivalent to suffixation in human language. Publisher PDF

International audience; How did human communication evolve from an animal-like vocal system to spoken language? Research on primate communication in particular has produced a wealth of data, which highlight the various evolutionary continuities and discontinuities between animal and human communication. Research topics include the mechanisms and flexibility of sound production, how different call units are assembled into complex utterances, how meaning is extracted from vocal structures, and how the psychological mechanisms underlying animal call production and comprehension compare to those of humans. The purpose of this chapter is to present the state-of-the-art of these various strands of research and to show how methodological tools of linguistics can help decipher animal communication.

Call rate can be a salient feature in animal communication. Depending on the species, different psychological variables appear to influence call rates but the exact nature of these relationships remains poorly explored. Here, we demonstrate for free-ranging Campbell's monkeys that the call rates of four different alarm series (termed H, K, K+, and B series) vary systematically as a function of context, associated behaviour, and identity of the caller. K+ series were given more rapidly to predation than non- predation events, K+ and K series more rapidly to visual than auditory predator detection, and H series more rapidly while counterattacking an eagle than staying put. Finally, there were individual differences in B series, suggesting that call rate potentially provides listeners with cues about the caller's anti-predator behaviour, event type experienced, and his identity.

International audience; One accepted function of vocalisations is to convey information about the signaller, such as its age-sex class, motivation, or relationship with the recipient. Yet, in natural habitats individuals not only interact with conspecifics but also with members of other species. This is well documented for African forest monkeys, which form semi-permanent mixed-species groups that can persist for decades. Although members of such groups interact with each other on a daily basis, both physically and vocally, it is currently unknown whether they can discriminate familiar and unfamiliar voices of heterospecific group members. We addressed this question with playbacks on monkey species known to form polyspecific associations in the wild: red-capped mangabeys, Campbell's monkeys and Guereza colobus monkeys. We tested subjects' discrimination abilities of contact calls of familiar and unfamiliar female De Brazza monkeys. When pooling all species, subjects looked more often towards the speaker when hearing contact calls of unfamiliar than familiar callers. When testing De Brazza monkeys with their own calls, we found the same effect with the longest gaze durations after hearing unfamiliar voices. This suggests that primates can discriminate, not only between familiar and unfamiliar voices of conspecifics, but also between familiar and unfamiliar voices of heterospecifics living within a close proximity.

International audience; A standard way of describing the vocal behaviour of nonhuman primates is to classify the vocal repertoire as either graded or discrete. We analysed a large database of calls given by adult males of a primate considered a typical example for discrete vocal behaviour, the forest-dwelling Campbell's monkeys, Cercopithecus campbelli. We recorded vocal responses from several dozen individuals to their main predators, crowned eagles and leopards. Using cluster analysis techniques, we found two main call types, which were modified further by optional affixation of an inflexible vocal structure. It was possible to force the four call types into eight subtypes, with various degrees of gradedness. When taking context into account, we found that acoustically discrete and nonaffixed calls tended to be given right after discovering a predator, while acoustically graded and affixed calls were given during later parts of a predator encounter and to nonpredatory disturbances. In sum, our results suggest that classifications of primate vocal repertoires as either discrete or graded are likely to be meaningless, as communicatively relevant acoustic variation can be present within seemingly discrete call types.

This paper reports on an automated and openly available tool for automatic acoustic analysis and transcription of primate calls, which takes raw field recordings and outputs call labels time-aligned with the audio. The system's output predicts a majority of the start times of calls accurately within 200 milliseconds. The tools do not require any manual acoustic analysis or selection of spectral features by the researcher.

We would like to thank the French Ministère de l’Enseignement Supérieur et de la Recherche (PhD grant to SK), the Université de Saint-Etienne (research sabbaticals to FL and NM, visiting professorship to KZ and research funding) and the European Research Council (KZ grant PRILANG 283871). Long-term social recognition is vital for species with complex social networks, where familiar individuals can encounter one another after long periods of separation. For non-human primates who live in dense forest environments, visual access to one another is often limited, and recognition of social partners over distances largely depends on vocal communication. Vocal recognition after years of separation has never been reported in any great ape species, despite their complex societies and advanced social intelligence. Here we show that bonobos, Pan paniscus, demonstrate reliable vocal recognition of social partners, even if they have been separated for five years. We experimentally tested bonobos' responses to the calls of previous group members that had been transferred between captive groups. Despite long separations, subjects responded more intensely to familiar voices than to calls from unknown individuals - the first experimental evidence that bonobos can identify individuals utilising vocalisations even years after their last encounter. Our study also suggests that bonobos may cease to discriminate between familiar and unfamiliar individuals after a period of eight years, indicating that voice representations or interest could be limited in time in this species. Publisher PDF

International audience; 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

International audience; Habitat type, predation pressure and reproductive interests are all thought to determine the anti-predator behaviour of non-primates, but only few systematic studies exist. Here, we experimentally elicited anti-predator behaviour in six different groups of forest-living Campbell's monkeys, using visual and acoustic models of leopards, crowned eagles, and snakes. Individuals produced a variety of anti-predator behaviours, depending on the type of predator and whether or not it was visible. Adult males generally behaved conspicuously, either by attacking eagles or producing threat behaviours at a distance to leopards. Adult females remained cryptic to eagles, but joined their male in approaching leopards. To snakes, both males and females responded strongly to familiar Gaboon vipers, but far less to unfamiliar black mambas. Finally, if a predator could only be heard, both males and females produced fewer alarm calls and often changed their vertical position in the canopy (upwards for leopards; downwards for eagles), despite all predator vocalisations being presented from the ground. We concluded that Campbell's monkeys display sex-specific anti-predator behaviours, which are largely driven by the predators' hunting techniques, mode of predator detection and the forest habitat structure

International audience; Bonobos live in dense forest habitats where visual communication is often limited rendering vocal signals important to regulate their social interactions. Moreover their fluid fission-fusion society requires contact over long distances, suggesting that vocal signals of group members are recognised individually. To this end, individual signatures should be reliably encoded in vocal interactions and memorised by recipients over long periods. In this study we investigated individual vocal recognition of group members that had been separated for long periods of time (two to nine years) with varying relationships. In the wild, long-term separation happens regularly, usually in relation to female migration. In captivity, the same process takes place during the transfer of individuals between zoos, mimicking wild migration. We simulated bonobo transfers by broadcasting contact calls of familiar or unfamiliar individuals to our subjects, thus imitating the arrival of new group members. In total, we tested 15 bonobos (> 10 years old) from three European zoos and compared their behavioural responses. We found that bonobos responded differently to familiar voices than to stranger voices, even after prolonged separation. However, the recognition of past partners appears to diminish after being separated for 6-8 years. This interesting result will be discussed regarding to the social needs in bonobos.

International audience; We develop a formal semantic analysis of the alarm calls used by Campbell’s monkeys in the Tai forest (Ivory Coast) and on Tiwai island (Sierra Leone)—two sites that differ in the main predators that the monkeys are exposed to (eagles on Tiwai vs. eagles and leopards in Tai). Building on data discussed in Ouattara et al. (PLoS ONE 4(11):e7808, 2009a; PNAS 106(51): 22026–22031, 2009b and Arnold et al. (Population differences in wild Campbell’s monkeys alarm call use, 2013), we argue that on both sites alarm calls include the roots krak and hok, which can optionally be affixed with -oo, a kind of attenuating suffix; in addition, sentences can start with boom boom, which indicates that the context is not one of predation. In line with Arnold et al., we show that the meaning of the roots is not quite the same in Tai and on Tiwai: krak often functions as a leopard alarm call in Tai, but as a general alarm call on Tiwai. We develop models based on a compositional semantics in which concatenation is interpreted as conjunction, roots have lexical meanings, -oo is an attenuating suffix, and an all-purpose alarm parameter is raised with each individual call. The first model accounts for the difference between Tai and Tiwai by way of different lexical entries for krak. The second model gives the same underspecified entry to krak in both locations (= general alarm call), but it makes use of a competition mechanism akin to scalar implicatures. In Tai, strengthening yields a meaning equivalent to non-aerial dangerous predator and turns out to single out leopards. On Tiwai, strengthening yields a nearly contradictory meaning due to the absence of ground predators, and only the unstrengthened meaning is used.

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Background. Some human immunodeficiency virus (HIV)-infected individuals initiating combination antiretroviral therapy (cART) with low CD4 counts achieve viral suppression but not CD4 cell recovery. We aimed to identify (1) risk factors for failure to achieve CD4 count >200 cells/μL after 3 years of sustained viral suppression and (2) the association of the achieved CD4 count with subsequent mortality.Methods. We included treated HIV-infected adults from 2 large international HIV cohorts, who had viral suppression (≤500 HIV type 1 RNA copies/mL) for >3 years with CD4 count ≤200 cells/μL at start of the suppressed period. Logistic regression was used to identify risk factors for incomplete CD4 recovery (≤200 cells/μL) and Cox regression to identify associations with mortality.Results. Of 5550 eligible individuals, 835 (15%) did not reach a CD4 count >200 cells/μL after 3 years of suppression. Increasing age, lower initial CD4 count, male heterosexual and injection drug use transmission, cART initiation after 1998, and longer time from initiation of cART to start of the virally suppressed period were risk factors for not achieving a CD4 count >200 cells/μL. Individuals with CD4 ≤200 cells/μL after 3 years of viral suppression had substantially increased mortality (adjusted hazard ratio, 2.60; 95% confidence interval, 1.86-3.61) compared with those who achieved CD4 count >200 cells/μL. The increased mortality was seen across different patient groups and for all causes of death.Conclusions. Virally suppressed HIV-positive individuals on cART who do not achieve a CD4 count >200 cells/μL have substantially increased long-term mortality. © The Author 2014.

International audience; How did human language evolve from earlier forms of primate communication? One key transition has been increased motor control during vocalisation, which enables humans to generate and imitate complex vocal patterns. Although humans are unique in this way, evolutionary inventions are usually modifications of earlier adaptations. The purpose of this chapter thus is to survey the recent primate literature for evidence of vocal control. To this end, we are interested in two qualities, acoustic variants of basic call types and call sequences. We find evidence for both in different species of primates, suggesting a direct transition from primate vocal behaviour to human speech. Future research will have to focus on the mechanisms of motor control of the speech-relevant articulators, particularly the larynx, velum, tongue, and lips.

International audience; The book presents new and stimulating approaches to the study of language evolution and considers their implications for future research. Leading scholars from linguistics, primatology, anthroplogy, and cognitive science consider how language evolution can be understood by means of inference from the study of linked or analogous phenomena in language, animal behaviour, genetics, neurology, culture, and biology. In their introduction the editors show how theseapproaches can be interrelated and deployed together through their use of comparable forms of inference and the similar conditions they place on the use of evidence. The Evolutionary Emergence of Language will interest everyone concerned with this intriguing and important subject, including those in linguistics, biology, anthropology, archaeology, neurology, and cognitive science

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National audience; Quelles sont les racines phylogénétiques de la capacité de l’Homme à contrôler sa production vocale tout en apprenant des autres? Cette capacité ne fait pas clairement partie des caractéristiques traditionnellement associées à la communication vocale des primates non humains, même si de récentes découvertes en neurobiologie ont révélé qu’une prédisposition à un contrôle moteur de la production vocale semblait exister. Ici, nous avons étudié la capacité à modifier la structure acoustique d’un cri sous influence sociale chez deux espèces de cercopithèques forestiers sauvages. Tout d’abord, nous avons étudié la relation entre les affinités sociales et la similarité vocale des cris de contact chez les femelles mone de Campbell. Nous avons trouvé une corrélation significativement positive entre la force du lien social et le degré de similarité acoustique des cris, indépendamment du degré de proximité génétique, suggérant que les développements vocaux et sociaux sont liés. Dans un second temps, nous avons étudié la capacité des femelles Diane à modifier de manière immédiate la structure de leurs cris de contact pour s’adapter au contexte social, un phénomène connu chez l’Homme sous le terme d’accommodation vocale. Les femelles divergent vocalement les unes des autres lorsqu’elles se déplacent dans un habitat où les conditions de visibilité sont mauvaises, mais convergent au moment des interactions vocales affiliatives. Une femelle répond à une autre en utilisant une structure acoustique similaire. Même si des facteurs génétiques semblent déterminer le répertoire général d’une espèce, certains types de cris restent modifiables grâce à un apprentissage vocal socialement guidé, suggérant que l’évolution du langage pourrait être le fruit d’un processus semblable.

International audience; Acoustic variability and individual distinctiveness of vocal signals are expected to vary with both their communicative function and the need for individual recognition during social interactions. So far, few attempts have been made to comparatively study these features across the different call types within a species' vocal repertoire. We collected recordings of the six most common call types from 14 red-capped mangabeys (Cercocebus torquatus) to assess intra- and interindividual acoustic variability, using a range of temporal and frequency parameters. Acoustic variability was highest in contact and threat calls, intermediate in food calls, and lowest in loud and alarm calls. Individual distinctiveness was high in contact, threat, loud and alarm calls, and low in food calls. In sum, calls mediating intragroup social interactions were structurally most variable and individually most distinctive, highlighting the key role that social factors must have played in the evolution of the vocal repertoire in this species. We discuss these findings in light of existing hypotheses of acoustic variability in primate vocal behavior.

Individually distinct vocalizations are widespread among social animals, presumably caused by variation in vocal tract anatomy. A less-explored source of individual variation is due to learned movement patterns of the vocal tract, which can lead to vocal convergence or divergence in social groups. We studied patterns of acoustic similarity in a social call produced by 14 female Diana monkeys ( Cercopithecus diana ) in two free-ranging groups. Calls showed variability in fundamental frequency contours owing to individual identity and external context. Vocal divergence increased significantly between females during poor visibility and tended to increase in the presence of neighbours. In contrast, vocal convergence increased significantly between females during vocal interactions, because females matched the frequency contour of their own call with another female's preceding call. Our findings demonstrate that these primates have some control over the acoustic fine structure of their most important social vocalization. Vocal convergence and divergence are two opposing processes that enable callers to ensure spatial proximity and social cohesion with other group members.

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Background Non-human primate communication is thought to be fundamentally different from human speech, mainly due to vast differences in vocal control. The lack of these abilities in non-human primates is especially striking if compared to some marine mammals and bird species, which has generated somewhat of an evolutionary conundrum. What are the biological roots and underlying evolutionary pressures of the human ability to voluntarily control sound production and learn the vocal utterances of others? One hypothesis is that this capacity has evolved gradually in humans from an ancestral stage that resembled the vocal behavior of modern primates. Support for this has come from studies that have documented limited vocal flexibility and convergence in different primate species, typically in calls used during social interactions. The mechanisms underlying these patterns, however, are currently unknown. Specifically, it has been difficult to rule out explanations based on genetic relatedness, suggesting that such vocal flexibility may not be the result of social learning. Results To address this point, we compared the degree of acoustic similarity of contact calls in free-ranging Campbell's monkeys as a function of their social bonds and genetic relatedness. We calculated three different indices to compare the similarities between the calls' frequency contours, the duration of grooming interactions and the microsatellite-based genetic relatedness between partners. We found a significantly positive relation between bond strength and acoustic similarity that was independent of genetic relatedness. Conclusion Genetic factors determine the general species-specific call repertoire of a primate species, while social factors can influence the fine structure of some the call types. The finding is in line with the more general hypothesis that human speech has evolved gradually from earlier primate-like vocal communication.

International audience; In contrast to humans, non-human primates are famously unable to control their vocal behavior, learn new utterances, and combine existing ones in creative ways. However, recent studies have shown that, despite strong genetic control, acoustic plasticity exists in several primate calls. For example, many forest dwelling species rely strongly on vocal signals, with calls used to regulate social behavior showing considerable degrees of acoustic flexibility. Our ongoing research with free-ranging Diana monkeys (Cercopithecus diana diana) of Taï National Park, Ivory Coast, is designed to examine the influences of various social and environmental factors on the evolution of acoustic flexibility in these monkeys’ vocal repertoire. Diana monkeys are known for their ability to produce referential alarm calls but little is known about females’ close-range vocalizations. A first field study conducted in 2009 has revealed that adult females emit several acoustically and contextually distinct subtypes of contact calls. Social and environmental factors, such as group activity, proximity to neighbors, or general visibility, were significantly related to a structural classification based on acoustic parameters. We are currently investigating the potential function of the different subtypes. Data are collected at the individual level using focal sampling on adult females of two fully habituated free-ranging Diana monkey groups. We will examine a number of potential social and environmental functions (e.g. spatial cohesion, social bonding, habitat visibility) to investigate which ones have led to the evolution of acoustic flexibility and which ones have had no impact.

International audience; Human language is too complex to have emerged without any evolutionary precursors. Our research on the vocal behaviour of forest guenons (Cercopithecus spp) has revealed a number of possible precursors that may have been important as building blocks in human language evolution. First, despite a rigid species-specific vocal repertoire, there is considerable acoustic plasticity in some calls of Campbell’s monkeys, which is related to the social function of the calls. For example, contact call variants of females are more similar between preferred than not preferred partners, suggesting a process of vocal sharing. Second, contact calls also take part in conversation-like vocal exchanges that are socially controlled. Third, several guenon species produce acoustically distinct calls to specific external events. For example, Campbell’s monkeys produce acoustically different alarm calls to the same predator. Calls are meaningful within and between species. Female Campbell’s monkeys possess a complex alarm call repertoire, although there are interesting differences between captive and wild individuals. Males produce six call types that differ in frequency contour and in whether they have an acoustically invariable suffix. Suffixed calls carry a broader meaning than unsuffixed ones. Fourth, the six calls are concatenated into context-specific sequences, following basic combinatorial principles. Sequence composition, order, and rhythm enable males to inform about type and degree of danger, predator class, as well as some environmental and social events. Data suggest that a strong dichotomy between human language and nonhuman primate vocal communication is no longer tenable.

8th International Conference on the Evolution of Language (EVOLANG 8), Utrecht, NETHERLANDS, APR 14-17, 2010; International audience; Human language is too complex to have emerged in the absence of any evolutionary precursors, which suggests that primitive forms of pre-linguistic communication can be found in animals. Whether this was based on acoustic or gestural communication is an ongoing debate. An argument against a vocal origin is the absence of vocal flexibility and complexity in non-human primates. However, human language is primarily a vocal behaviour, and vocal flexibility – as assessed by vocal plasticity, semanticity, compositionality, and intentional signalling - is not a uniquely human trait. Our research focuses on the precursors of the various types of vocal flexibility in forest guenons (Cercopithecus spp). The vocal tract of nonhuman primates is in principle capable of producing speech-like sounds (Riede et al 2005) and one puzzle is why nonhuman primates do not make greater use of this feature. Instead, primates produce a finite range of calls that develop under strong genetic control. Within some call types, however, some flexibility can be seen at the level of call morphology, as for example demonstrated by socially-determined vocal plasticity and vocal sharing in Campbell's monkey contact calls used in conversation-like socially controlled vocal exchanges (Lemasson & Hausberger 2004; Lemasson et al 2010). Second, many primates produce acoustically distinct calls to specific external events, including Diana and Campbell's monkeys. In both species, the adult males and females produce acoustically different alarm calls to the same predator (Ouattara et al 2009a), but calls are meaningful to others, both within and between species. Alarm calls are not only predator-specific but also vary depending on the modality by which the predator is discovered, i.e. the visual or acoustic domain. In Campbell's monkeys females produced a complex alarm call repertoire, although differences were found between captive and wild individuals. Captive ones did not produce predator-specific calls but had a unique call to humans (Ouattara et al 2009a). For males, we found a repertoire of six call types, which could be classified into different morphs, according to the frequency contour and whether calls were trailed by an acoustically invariable suffix. Suffixed calls carried a broader meaning than unsuffixed ones (Ouattara et al 2009b). The six calls were concatenated into context-specific call sequences, following basic combinatorial principles (Ouattara et al 2009c). In sum, the vocal abilities in guenons go significantly beyond the currently assumed default case for nonhuman primates. Flexibility can be seen at all relevant levels, including limited control over call morphology, conversational rules, ability to produce context-specific calls, and some basic combinatorial properties. The data are at odds with a gestural origins of language theory. Gestural signals do not appear to play a key role in these species, while vocal flexibility is seen in all key components despite the fact that they have split from the human line about 30 million years ago. Field playback experiments will be needed to confirm whether receivers utilise these rich patterns to guide their behavioural decisions. But even in the absence of such evidence data suggest that a strong dichotomy between human language and nonhuman primate communication may no longer be tenable in the vocal domain. The visually dense forest habitat may have played a key role in the evolution of advanced vocalisation skills.

International audience; According to most current theories, one of the main differences between human speech and animal vocal communication concerns syntax. In searching for the origins of syntactic communication, we analysed the loud call behaviour of free-ranging Campbell's monkey males. Using two years of naturalistic observations and predator-simulation experiments, we were able to distinguish six basic alarm call types. Acoustic variation to discriminate between the different calls was achieved by frequency modulation (Boom, Krak, Hok) and affixation, i.e., the facultative addition of an acoustic suffix (Krak-oo, Hok-oo, Wak-oo). Moreover, when responding to a disturbance, males rarely produce signle calls, but usually generated sequences of 2 to 40 calls. From the analysis of 250 calling events, we identified six contextually-determined calling sequences, which varied in terms of call type composition, order of succession, and rhythm of delivery. These levels of organization appear to encode information about the type and urgency of the danger, as well as the caller's associated behaviour. Preliminary playback experiments confirmed that affixation and call combination were discriminated by females. Our findings suggest that early precursors of syntactic communication may already have been present in the common ancestor of modern non-human primates and humans.

International audience; Bien que des études aient été menées sur les propriétés sémantiques des cris forts des cercopithèques mâles, le répertoire vocal des femelles reste très peu connu. Elles forment pourtant le noyau du groupe social, dont l’organisation repose sur des échanges vocaux fréquents dans un habitat visuellement limité. La fonction de ces échanges vocaux est encore largement incomprise à l’heure actuelle, mais les paramètres physiques et sociaux de l’environnement semblent influencer fortement la structure acoustique des cris. Nous avons testé cette hypothèse chez deux groupes de singes Diane habitués (Parc National de Taï, Côte d’Ivoire), au sein desquels neuf femelles adultes ont été observées pendant 3 mois. Des analyses acoustiques et contextuelles ont révélé l’existence de plusieurs types et sous-types de cris. En effet, les femelles émettent un type de cri d’alerte en réponse à diverses perturbations de l’environnement, ainsi qu’un type de cri de cohésion qui comporte plusieurs sous-types. L’émission de ces sous-types varie en fonction de facteurs sociaux (position dans le territoire, activité du groupe, rencontre intergroupe) ainsi que des propriétés de l’habitat (luminosité, densité de la végétation). Par ailleurs, le sous-type associé aux contextes où la cohésion sociale doit être renforcée (visibilité réduite, compétition intergroupe, période d’activité sociale et de repos) présente des différences acoustiques individuelles. Nos résultats suggèrent que la difficulté d’étudier les cris de faible intensité des singes forestiers a conduit à sous-estimer la complexité de leurs capacités de communication.

International audience; Field studies on male forest guenon alarm-calling behaviour have revealed a number of intricacies about how these primates use vocalizations to protect themselves from predation. In these species, the vocal behaviour of adult females is often different from that of the males, but little systematic work has been done. Here, we describe the alarm call system of female Campbell's monkeys, Cercopithecus campbelli, in their natural forest habitat in western Ivory Coast. We found that in response to disturbing events, females produced three basic alarm call types, ‘wak-oos’, ‘hoks’ and acoustically variable ‘trill’ calls, consisting of repeated and rapidly ascending (RRA) pulses, which varied systematically in the temporal and frequency domains. Using observational and experimental data we were able to demonstrate that the RRA calls consisted of four acoustic variants, which could be associated with specific contexts, allowing listeners to draw inferences about the type of disturbance experienced by the caller. We also compared the alarm call behaviour of free-ranging individuals with published results from captivity. As predicted, captive individuals failed to produce predator-specific alarm calls, but they also produced an RRA variant in response to humans that was absent in the wild. We discuss the relevance of these findings in terms of their broader potential impact on evolutionary theories of primate communication.

International audience; Our research describes the natural communication in different primates, as well as their underlying cognitive abilities. We are interested in the communication skills and social cognition of monkeys and apes in their natural habitats. For this purpose, we observe wild groups in Africa and Asia during their daily activities in order to understand what communication signals they are able to produce, under what circumstances they produce them, and what sorts of responses they elicit from listeners. Once we have gathered enough information to suspect a relationship between a particular call type, a set of events and a typical response, we conduct a field playback experiment to determine the call’s meaning. During such an experiment we play back a recorded example of a particular call to a naïve receiver in order to study its response. For example, chimpanzees produce different types of food grunts depending on the type of food they find, such as apples or bread. We found that these calls were indeed meaningful to other chimpanzees. For instance, if we played back recordings of ‘apple grunts’ listeners were more likely to look for food in places where they previously found apples, but not bread, and vice versa. In another study, we found that some monkeys are able to combine some of their vocalizations in systematic ways to create different combinations with separate meanings. Our playback experiments showed that it was the combinations of calls, rather than the individual calls themselves, which carried the meaning, an example of simple primate ‘grammar’.

International audience; Le répertoire vocal des cercopithèques présente un important dimorphisme sexuel car les femelles ne possèdent pas de sacs vocaux que les mâles utilisent pour produire des cris forts et graves adaptés aux contraintes de propagation dans la forêt. La complexité des cris d’alarme des mâles et leur capacité dans la communication référentielle et dans la combinaison de cris ont fait l’objet de plusieurs études récentes. Inversement, le système des cris d’alarme des femelles est peu connu, probablement parce qu'elles sont difficiles à observer et à enregistrer dans leur habitat forestier. Pourtant, un niveau élevé de plasticité acoustique a été décrit chez les femelles captives mones de Campbell (Cercopithecus campbelli). Elles possèdent un répertoire vocal riche, composé de 10 types de cris dont certains présentent 2 à 6 sous-types. Un partage vocal de variantes de cri de contact a été observé entre certaines femelles adultes affiliées. En captivité, leurs cris d’alarmes peuvent être classés en deux sous-types différents selon leur structure et leur contexte de production (RRA2 – au passage d’un humain et RRA1 - pour tout autre type de danger). Ce travail est le résultat de deux années d’étude de terrain sur deux groupes de mones de Campbell, habitués à la présence humaine, du parc national de Taï (Côte d'Ivoire). Des observations comportementales des contextes naturels d’émission vocale des femelles adultes et des analyses acoustiques nous ont permis de décrire 3 types de cris d’alarmes fréquents et 2 types rares. Deux types de cris fréquents (RRA3, RRA4), jamais enregistrés en captivité, étaient utilisés dans un contexte de prédation, respectivement en réponse à la présence de léopards et d’aigles. RRA1 était utilisé, comme en captivité, pour des dangers de nonprédation (p. ex. en descendant à une strate inférieure ou effrayé par un mouvement brusque d’oiseau), tandis qu'aucun RRA2 n’a été enregistré. Nous avons également enregistré des cris d’alarmes rares qui ressemblent fortement à ceux qui sont produits par le mâle et qui sont principalement émis dans des contextes de forte menace de prédation. Une série d'expériences (présentation de modèles empaillés et repasse de cris de prédateurs) a permis de confirmer l'existence de deux types de cris différents pour le léopard et l'aigle, et de suggérer que les femelles, au-delà de la simple référence au type de prédateur, pourraient transmettre des informations supplémentaires sur le degré de menace. Cette étude confirme le niveau élevé de variabilité acoustique décrit en captivité chez les mones de Campbell, mais met également en lumière quelques différences importantes entre animaux sauvages et captifs.

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