Communication styles in bonobos and chimpanzees: Same same but different?

Comparative studies in relation to language origins have mainly focused on our closest living relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Direct comparisons however are still lacking and/or concerned individuals living in captive environments only. Here, we carried out a systematic, quantitative comparison of communicative abilities of bonobos and chimpanzees living in four different communities in the wild with a special focus on within- and between-species variability. The analyses focused on communicative exchanges between mother-infant dyads to initiate joint travel. The communicative behavior of twelve bonobo (LuiKotale, Wamba; DRC) and thirteen chimpanzee mother-infant dyads (Taï South, Côte d’Ivoire; Kanyawara, Uganda) was filmed during a total of 1033 (bonobos) and 1189 (chimpanzees) hours of observation. We analyzed ‘signal-response’ structures (e.g. response waiting, gestural sequences, temporal relationships) in 316 bonobo and 415 chimpanzee carry initiations, while taking into account dyadic role, infant age and site. Differences in behavior could not be attributed to within-species variability. Bonobos solicited carries more frequently from shorter distances and via coordinated responses. Chimpanzees used a higher frequency of response waiting and sequences, showing overall more persistence. Our findings suggest that interactional intelligence paved the way to language with communication styles being influenced by social matrices.