In contrast, during grooming bouts, groomers produced ELSs to request reciprocation of grooming from their partner. Individuals who produced the signal to initiate grooming were likely to offer grooming. Further exploration into alternative functions of ELSs in the Kanyawara community revealed that, in this community, this signal functions to initiate grooming bouts and to reengage partners during grooming pauses. This suggests that ELSs do not function referentially at these sites, and the published findings from Ngogo were not replicated. At the latter sites this response occurred at low rates and signallers did not seem to pursue this goal. Our data show that scratchers were significantly more likely to receive grooming in the scratched location at Ngogo compared to the other three sites. Hence here, we compared whether ELSs are used in a referential manner across four wild communities of eastern chimpanzees (Ngogo, Kanyawara, Sonso and Waibira). This study suggested continuity between referential abilities in humans and our closest living relatives, making it an important finding to replicate in other populations. Apes, living in their natural environments, rarely or never point, but it has been claimed that male chimpanzees, Pan troglodytes schweinfurthii, from the Ngogo community, Uganda, habitually use exaggerated loud scratches (ELSs) to refer to specific body locations where they wish to be groomed (Pika & Mitani, 2006, Current Biology, 16(6), 191–192). A fundamental aspect of human communication is our ability to refer to external objects and events through both words and gestures (such as pointing), yet the evolutionary origins of such signals remain obscure.

Free monkey sounds