Thermal imaging reveals audience-dependent effects during cooperation and competition in wild chimpanzees

Funding from the Royal Zoological Society of Scotland, the Fond des Donations of the University of Neuchâtel, and the Swiss National Science Foundation (Project Number 310030_185324 to K.Z.) are gratefully acknowledged. The research further benefitted from funding from the NCCR Evolving Language (SNSF 51NF40_180888).Accessing animal minds has remained a challenge since the beginnings of modern science. Here, we used a little-tried method, functional infrared thermal imaging, with wild chimpanzees during common social interactions. After removing confounds, we found that chimpanzees involved in competitive events had lower nose skin temperatures whereas those involved in cooperative events had higher temperatures, the latter more so in high- than low-ranking males. Temperatures associated with grooming were akin to those of cooperative events, except when males interacted with a non-reciprocating alpha male. In addition, we found multiple audience effects. Notably, the alpha male’s presence reduced positive effects associated with cooperation, whereas female presence buffered negative effects associated with competition. Copulation was perceived as competitive, especially during furtive mating when other males were absent. Overall, patterns suggest that chimpanzees categorise ordinary social events as cooperative or competitive and that these perceptions are moderated by specific audiences.Publisher PDFPeer reviewe