Communication and Travel Coordination in Wild Bonobos
Group movement is often governed by simple, decentralized rules. From swarming locusts to crowds of commuters, self-organization often eliminates the need for a more explicit form of coordination. Passive, local cues, however, cannot explain group movement in many circumstances, especially among populations exhibiting low spatial cohesion and highly differentiated social relationships. The research presented in this dissertation examines communication and travel patterns of wild bonobos (Pan paniscus), a species of great ape with a highly fluid ‘fission-fusion’ social structure, in which individuals from a single social group regularly divide into smaller subgroups (‘parties’). In Chapters 1 and 2, we investigate the long-distance vocalizations that bonobos use to communicate between separated parties. We find that call combinations, but not single call types alone, were associated with particular patterns of inter-party movement. Specifically, individuals who were highly motivated to approach and join another party produced ‘whistle-high hoot’ combinations, while individuals motivated to recruit others to their own party produced distinct ‘low hoot-high hoot’ combinations. In Chapter 3, we turn our focus to ‘branch drag’ displays, a form of within-party communication. Bonobos performed these displays before traveling to distant feeding trees, but not prior to shorter bouts of travel, thus potentially providing individuals with information about subsequent group movement. Results from all three chapters demonstrate that bonobos use particular signals to facilitate movement patterns that are typical of fission-fusion societies. Furthermore, we suggest that the unpredictable nature of such a social structure may have favored individuals who are able to flexibly produce signals related to movement in order decrease the uncertainty associated with fission-fusion dynamics, and thereby reduce the costs of group coordination.