No abstract

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 audienceRecognizing 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

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.

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.