Who waits when? Age and interactional context shape turn-taking timing in sooty mangabeys (Cercocebus atys) in the wild

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Introduction The evolution of language still remains a mystery. A recent hypothesis proposed that the cooperative mechanism of turn-taking may have predated language and represents an interactional scaffold from which language evolved. Testing this hypothesis requires systematic studies of turn-taking systems in closely related species that examine features directly comparable to human conversational organization, including multimodal exchange, composite turns, and adaptation to recipient characteristics. However, methodological approaches for examining these features in nonhuman primates remain limited. To address this gap, we examined turn-taking in 21 adult female sooty mangabeys ( Cercocebus atys ) living in Taï National Park, Côte d’Ivoire. Sooty mangabeys provide a useful model system because vocal and multimodal turn-taking have been documented in this species, and social factors shape their interactions. We addressed two research questions: (1) How is turn-taking organized in interactions of adult female sooty mangabeys? (2) Is signal-based turn-taking timing influenced by socio-demographic factors? Methods We collected video and behavioral data across three field seasons, from May 2022 to March 2024. This resulted in 407.17 hours of focal observation, an average of 18.51 hours per female, 117.98 hours of video recordings, and an average of 5.36 hours per female. From these recordings, we analyzed a total of 226 interactions based on distinct selection criteria (mean of 20.55 interactions/female), across five different contexts (affiliative, agonistic, feeding, grooming, and sexual contexts). We used a novel approach that quantified composite turns composed of actions, gestures, facial expressions, and vocalizations. We examined turn size, turn composition, and turn transitions and gap durations within signal-based exchanges. We then tested whether timing within signal-based exchanges varied with initiator age and rank, social relationship strength, and interactional context. Results The results showed that turn-taking was organized differently across contexts. Signal-exchange gaps were generally short, and initiator age influenced gap duration in affiliative interactions only. Discussion These findings suggest that turn-taking in adult female sooty mangabeys is multimodal, context-dependent, and partly socially structured, consistent with the hypothesis that core organizational features of conversational turn-taking predate human language.

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