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Table S1. Group composition and individual characteristics of spider monkeys (Ateles geoffroyi) in the Otoch Ma'ax Yetel Kooh reserve, Yucatan Peninsula, Mexico. Table S2. Results of each statistical model and Post hoc (Turkey test) comparisons. All assumptions for the GLMM analyses were met (collinearity and overdispersion). Table S3. Post-hoc comparison for the analysis of fission-fusion events vs. call rate. Results of each statistical model and Post hoc (Turkey test) comparisons. All assumptions for the GLMM and GLM analyses were met (collinearity and overdispersion). Table S4. Post-hoc comparison for the analysis of changes in audience composition on call vs. call rate. Results of each statistical model and Post hoc (Turkey test) comparisons. All assumptions for the GLMM and GLM analyses were met (collinearity and overdispersion).

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

International audience; Conversation rules such as overlap avoidance and coordinated overlap have been reported in nonhuman animals, and seem to be adaptive responses to the requirements of social life. Some species display both patterns in an apparently flexible way, but the social factors mediating their respective usage remain poorly documented. We investigated the potential social factors guiding the usage of these temporal rules during collective howling in six free-ranging groups of black howler monkeys (Alouatta pigra). First, we found that adult males' vocalizations rarely overlap those of other callers while most adult females' calls overlap other members' calls, especially that of other females. Second, whereas some call types (notably affiliative calls) are typically emitted without overlap, roars (agonistic loud calls) overlap more frequently. Third, coordinated overlap is more frequent during intergroup competition. Our findings support the hypothesis that overlap avoidance and coordinated overlap are two different (here sex-related) vocal alliance social behaviors, at least for some nonhuman primates. More comparative investigations are now needed to explore further their evolutionary trajectories in this lineage.

International audience; Alouatta species utter the most powerful primate vocalizations in the Neotropics and are well-known for their loud and long-lasting male howling bouts. However, the diversity of acoustic structures used in these howling bouts, as well as in non-howling contexts, and the relative contribution of the different group members to the entire vocal repertoire, needed to be explored further. This report provides the first detailed description of the vocal repertoire of black howler monkeys (Alouatta pigra), focusing on acoustic structures and contexts of emission of both loud and soft calls as well as on the contribution rate of males and females to the different call types. Three free-ranging social groups of black howler monkeys living in Palenque National Park, Mexico were monitored. We identified twelve acoustically discriminable call types, eight described previously and four described here for the first time. A few call types were systematically emitted either isolated or during howling bouts, but most of them could be heard in both calling contexts. Three call types were emitted only by females and two only by males. Adult males’ call rates (for the seven shared call types) were higher than those of females but only when considering calls emitted within howling bouts. Our contextual analysis enabled us to divide call types into potential functional categories, according to their degree of contribution, to intra-group versus inter-group interactions and to neutral-positive versus negative situations. We then discussed how socio-ecological factors, notably sex differences in social behaviors, may explain the variability found in the vocal repertoire of this species and compared our findings with the literature on other primate species.

Social traditions based on communication signals are widespread in birds, cetaceans and humans, but surprisingly rare in nonhuman primates known for having genetically-determined vocal repertoires. This study presents the first description of a singular case of behaviour associated with calling (placing a hand in front of the mouth while vocalizing: HFM) in black howler monkeys. We showed, first, that HFM was found only in a subset of the groups observed, at the same geographical location and was age- and sex-specific. There was an audience effect on HFM, with highest rates when a neighbouring group was visible. HFM was non-randomly combined with audio-visual signals and always performed while roaring. High HFM rates triggered more vocal responses from group members and male neighbours and HFM signalers temporally synchronized their behaviour in a predictable way. Finally, the positioning of the hand systematically modified the call’s auditory structure. Altogether these results support the idea that HFM is an innovated, culturally transmitted communication signal that may play a role in inter-group competition and intra-group cohesion. This study opens new lines of research about how nonhuman primates developed strategies to overcome their constraints in acoustic plasticity very early in the primate lineage.

La reconnaissance auditive entre les membres d’un groupe est importante pour maintenir une cohésion socio-spatiale chez les espèces forestières où la visibilité dans l’habitat est limitée, mais cela peut aller au-delà du groupe chez les espèces territoriales avec la nécessité de reconnaître ses voisins. Nous avons évalué la capacité à reconnaître individuellement la voix de mâles voisins chez le singe hurleur noir "Alouatta pigra" sauvage au Mexique. Premièrement, nous avons effectué des enregistrements de hurlements spontanés de six mâles adultes, et démontré que le niveau de variabilité acoustique interindividuelle était bien supérieur au niveau de variabilité acoustique intra-individuelle. Deuxièmement, nous avons testé la reconnaissance auditive à l’aide d’un paradigme de violation des attentes basé sur la congruence spatiale des voix diffusées. Dans une population composée de six groupes de singes aux territoires adjacents, nous avons effectué des expériences de repasse par haut-parleur de hurlements. Chaque groupe a été testé dans deux conditions spatiales : cohérente (le haut-parleur est positionné du côté du territoire voisin approprié par rapport à la voix diffusée) et incohérente (le haut-parleur est positionné du côté du territoire opposé). Comme attendu, les individus ont présenté des réactions plus fortes pendant les situations incohérentes (vitesse d’approche, réponse vocale, comportements de marquage territorial). Ainsi, cette étude permet de confirmer l’existence d’un processus d’encodage et de décodage acoustique individuel chez cette espèce. Le paradigme utilisé, démontrant l’existence d’une carte mentale auditive du voisinage, va plus loin que les simples tests de discrimination classiquement utilisés, permettant de réellement parler de reconnaissance individuelle.

Erratum: We apologize for a mistake in Table 7. Speed listed in Table 7 (values for “Approach to speaker - Speed” in coherent situation) was erroneously calculated. The correct values are for coherent situation: 0.07 ± 0.05 and for incoherent situation: 0.23 ± 0.19. Results of GLMM are now Z = 6.1, P = 0.004.; International audience; Recognizing individuals auditorily is of primal importance in maintaining socio-spatial cohesion among conspecifics within a social group as well as for regulating space use among neighbours, particularly for species dwelling in forests where visual communication is constrained. This study evaluates the capacity of black howler monkeys (Alouatta pigra) in the Palenque National Park, Mexico, to recognize the voices of individual neighbours, using a violation-of-expectation paradigm based on the spatial congruence of voices. First, we assessed intra- vs inter-individual acoustic variations by comparing the acoustic structures of the loud calls of six adult males from three different social groups. Although the acoustic structures of barks were more individually discriminative than those of roars, both loud call types presented significant individual variations. Second, playbacks of sequences composed of barks and roars were studied in order to assess the auditory recognition capacity of six neighbouring groups. Two test situations were presented to each study group: the spatial location of the speaker was either congruent (in the appropriate neighbouring territory) or incongruent (in a territory on the opposite side) with the voice broadcast. Monkeys reacted significantly more (e.g. faster approach, more vocal responses) in incongruent situations. Our data suggest that black howler monkeys display individual acoustic variations and are capable of recognizing the voices of non-group members. Our experimental paradigm is an easily replicable way to investigate inter-group voice recognition in animals and to test the extent of socio-spatial cognitive abilities.

Recognizing individuals auditorily is of primal importance in maintaining socio-spatial cohesion among conspecifics within a social group as well as for regulating space use among neighbours, particularly for species dwelling in forests where visual communication is constrained. This study evaluates the capacity of black howler monkeys (Alouatta pigra) in the Palenque National Park, Mexico, to recognize the voices of individual neighbours, using a violation-of-expectation paradigm based on the spatial congruence of voices. First, we assessed intra- vs inter-individual acoustic variations by comparing the acoustic structures of the loud calls of six adult males from three different social groups. Although the acoustic structures of barks were more individually discriminative than those of roars, both loud call types presented significant individual variations. Second, playbacks of sequences composed of barks and roars were studied in order to assess the auditory recognition capacity of six neighbouring groups. Two test situations were presented to each study group: the spatial location of the speaker was either congruent (in the appropriate neighbouring territory) or incongruent (in a territory on the opposite side) with the voice broadcast. Monkeys reacted significantly more (e.g. faster approach, more vocal responses) in incongruent situations. Our data suggest that black howler monkeys display individual acoustic variations and are capable of recognizing the voices of non-group members. Our experimental paradigm is an easily replicable way to investigate inter-group voice recognition in animals and to test the extent of socio-spatial cognitive abilities.

Lemasson & Hausberger : Equal contribution; International audience; Nocturnal vocal activity in dolphins is often thought to be associated with feeding activity. However, when no food resources are available dolphins spend their time for the most part resting/sleeping. While unihemispherically sleeping, dolphins mostly swim slowly and synchronously in close proximity with one or more other individuals. Although vocal activity is lower during resting/sleeping, dolphins are not entirely silent the entire night. However, nothing is known about the temporal patterning of vocal activity at night and its potential relation with activity in dolphins. Here we recorded the vocal activity of a group of five captive bottlenose dolphins at night while having no feeding opportunity, examined whether there was any temporal pattern and/or a relation with breathing activity, used here as an index of overall activity. The temporal pattern revealed two peaks of intense whistle activity (8 p.m. and midnight), which were followed by a strong decrease of whistle rate and a slight decrease of respiration rate. We suggest that the high vocal activity at the peak periods might indicate socializing periods and that dolphins, like many other species, show periods of increased social and vocal interactions (chorusing?) before starting to rest/sleep, maybe to ensure the synchrony of slow swimming observed in this species. These findings contribute to a better understanding of nocturnal vocal activity in cetaceans and suggest new lines of research on vocal/social activity of dolphins in relation to presleep and resting behavior.

Alban Lemasson and Martine Hausberger have contributed equally to this work.; International audience; The mechanisms underlying vocal mimicry in animals remain an open question. Delphinidae are able to copy sounds from their environment that are not produced by conspecifics. Usually, these mimicries occur associated with the context in which they were learned. No reports address the question of separation between auditory memory formation and spontaneous vocal copying although the sensory and motor phases of vocal learning are separated in a variety of songbirds. Here we show that captive bottlenose dolphins pro-duce, during their nighttime resting periods, non-dolphin sounds that they heard during performance shows. Generally, in the middle of the night, these animals produced vocal copies of whale sounds that had been broadcast during daily public shows. As their life his-tory was fully known, we know that these captive dolphins had never had the opportunity to hear whale sounds before then. Moreover, recordings made before the whale sounds started being broadcast revealed that they had never emitted such sounds before. This is to our knowledge the first evidence for a separation between formation of auditory mem-ories and the process of learning to produce calls that match these memories in a marine mammal. One hypothesis is that dolphins may rehearse some special events heard during the daytime and that they then express vocally what could be conceived as a more global memory. These results open the way for broader views on how animals might rehearse life events while resting or maybe dreaming.