Third-party vocal intervention in the proboscis monkey (Nasalis larvatus)

Abstract Vocal intervention is a triadic social interaction, where third party responds vocally to conflict between group members, minimizing the costs of aggression in response intervention. Because there little information on vocal third-party nonhuman mammals, we investigated whether adult male proboscis monkeys use bray vocalization as signal intervene intragroup conflicts. First, audio-recorded 1,811 vocalizations from 17 free-ranging monkey groups Lower Kinabatangan Wildlife Sanctuary, analyzing 378 responses agonistic exchanges (shrieks) members. Second, video- and five habituated Labuk Bay Proboscis Monkey Sanctuary investigating context these dyads evoking support. We found that males one-male/multifemale mainly uttered vocalizations, whereas females, immatures, infants shrieks conflicts or other animal species. The significantly more often brays after than expected based overall occurrence brays. Brays ended 65% conflicts, which were accompanied by partners occurred females offspring. This suggests functions for resolution. suggest living high canopies tropical rainforest might restrict direct access prevent physical intervention, favoring evolution signal.