Datasets and R code

Investigating how non-human animals produce call sequences offers valuable insights into the evolutionary processes underlying meaning generation through vocal communication, including the origins of syntax. While a wide range of species combine calls into larger structures, often following specific rules, most studies focus only on one or a few sequences per species. This limits our understanding of animal abilities to combine calls and their potential to convey meaning through sequences. Our study addresses this gap by documenting the vocal sequence repertoire and their underlying rules in sooty mangabeys<i> (Cercocebus atys)</i>, a West African forest-dwelling monkey species. Over ten months, we collected data on two groups of wild sooty mangabeys in the Taï National Park, Ivory Coast. We recorded and annotated 1,672 recordings. We show that sooty mangabeys combine most of their calls, though they rely on a limited set of sequences. Within common sequences, we identified rules of call ordering and reoccurrence, as well as hierarchical structures. Interestingly, sooty mangabeys produced hierarchically structured sequences using only two call types, potentially generating a wide range of meanings. Our findings suggest that sooty mangabeys use both structured and unstructured sequences, each likely serving to convey specific information. While context of production, not addressed here, is essential for understanding the precise meaning of vocal utterances, our results underline the importance of a whole-repertoire approach in assessing the diversity of rule-based sequences, and hence the potential a vocal system has to expand meanings beyond the number of vocalisations in the repertoire.