Coordination of joint activities and communication in wild chimpanzees (Pan troglodytes) of the Budongo Forest, Uganda

Abstract

Evidence from captive studies suggests that chimpanzees (Pan troglodytes) lack the motivation to complete cooperative tasks and there is little evidence for communication that coordinates their behaviour during joint actions or whether individuals have a shared motivation towards the same goal. Two types of behaviour where individuals are argued to engage in joint activity are investigated in the Sonso community of wild chimpanzees in Budongo Forest Reserve, Uganda: joint travel and group hunting. This study presents evidence from naturalistic observations, and also a playback experiment to further investigate hunting behaviour. Joint travel appears to have no coordinating signal or behaviour on a local level, although the use of pant-hoot vocalisations to coordinate long-distance group travel is supported. In group hunting, bark vocalisations are associated with initiating a group hunt, indicating their potential role in coordination of joint action. Bark production also appears to be affected by the social composition of other hunters, with more barks being produced when other hunters are closer affiliates, suggesting flexibility in call production. The field experiment exploring joint action in group hunts utilises the alarm calls of the chimpanzees’ prey species- the Colobus monkey (Colobus guereza). Alarm calls produced by the monkeys when they were being hunting by chimpanzees and in response to an eagle stimulus were played back to dyads of affiliated males, and their vocal and behaviour responses recorded. Results firstly indicate that chimpanzees recognise different Colobus predator alarm. Furthermore, half of the trials with the Colobus hunting alarm elicited a vocal response of barks from both of the males in the experiment, along with joint movement in the direction of the playback. These initial results from a novel field experiment suggest that the bark vocalisation is associated with the initiation of joint action in the context of group hunting.