Social bonding, gestural complexity and displacement behaviour of wild chimpanzee

Kinship and demography affect social affiliation in many different contexts such as co-feeding, resting, travel, grooming, visual attention and proximity. Chimpanzees may coordinate these social interactions by using gestural communication to make signallers goal transparent to the recipient and also by increasing commitment of the recipient through including rewarding property in communication. The rewards of gesturing can be measured through the rates of displacement behaviour made in response to these gestures by the recipient. We tested hypothesis that gestural communication affects social affiliation after controlling for kinship and demography in wild, adult chimpanzees living in Budongo Forest, Uganda. We found that affiliative but not antagonistic gestures positively predicted social affiliation. Contexts differed in their association with gestures according to complexity and association with displacement behaviour. More complex, less intense gestures predicted mutual grooming, travel, visual attention whereas less complex, more intense gestures predicted unidirectional grooming. Mirroring these patterns, reduced displacement activity occurred in response to gestures associated with unidirectional grooming but not other contexts. We highlight that these tactical decisions that wild chimpanzees make in their use of gestural communication may be driven by complexity of social environment that influences effectiveness with which signalers can influence the recipient.