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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.

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.