A signal convention in natural chimpanzee communication

Human language relies on conventional signals that are arbitrary, stable, and socially transmitted. Whether other animals exhibit meaning-based communicative conventions is virtually unknown. Using a quasi-experimental design, we investigated this in chimpanzee unvoiced calls (UCs), such as acoustic raspberries, known to show usage variation. We collected audio and contextual data in 91 chimpanzees (0 to 55 y), across eight wild and captive groups that differed in the presence or absence of adult role models. Communities with role models emitted UCs in one dominant context, which remained stable over years and from first utterances in development (1 to 2 y old). In contrast, groups without role models displayed highly variable, unstable UC usage across contexts and years. This contextual variation could not be explained by age or by a shared emotional valence, and individuals could use different UC forms within the same context, suggesting a decoupling between the signal form and usage. Together, these findings provide evidence that chimpanzee UCs meet key criteria for a signal convention: arbitrary signal–usage mappings, social transmission, and stability within communities. These findings demonstrate that conventionalized communication is not a uniquely human feature but can also emerge through social learning mechanisms in other animals’ natural communication.