Do chimpanzees produce context-specific vocal structures in group-specific ways?

Abstract

Learning how to link a signal to its appropriate behavioural context in a flexible and meaningful way is foundational to human language, but there is little evidence of this capacity in nonhuman primates. We addressed this by studying chimpanzee, Pan troglodytes schweinfurthii, pant hoot contextual use in two communities, Sonso and Kanyawara, from two different wild populations in Uganda. Pant hoots are complex, composite vocal signals, comprising four acoustically distinct phases and produced in different contexts, mostly during travelling and feeding to mediate grouping dynamics. We measured 18 acoustic parameters across phase types and found significant effects of context in all four phases, confirming that pant hoots have the potential to inform others about the caller’s behaviour. We also found two interaction effects between context and community in the final let-down phase: Sonso males produced let-down call elements at higher rates during feeding than travelling and were also more likely to omit the let-down phase entirely during feeding than travelling, than Kanyawara males. We concluded that despite their largely fixed call repertoire, chimpanzees modulate acoustic features according to the behavioural context and, in the case of a few acoustic parameters, do so differently in different populations, with learning potentially involved in this process. Overall, however, the link between most of the acoustic features of chimpanzee calls and context seems to be largely independent of population, which contrasts with human language where different and novel signals are often flexibly attached to different information via social learning.