Examining variation in social behaviour and associated endocrine physiology across groups of the same species can help identify consistent hormone–behaviour interactions. We investigated differences in urinary oxytocin levels of individuals, of two neighbouring chimpanzee groups related to (a) socio-positive and -negative interaction frequencies, (b) within-group cooperation associated with between-group competition and (c) group-specific differences in urinary oxytocin reactivity of individuals in response to the same behavioural contexts. We found higher rates of cooperative group-level behaviours and larger relative party sizes in East Group males, while South Group males had higher non-directed aggression and copulation rates. Individuals of both groups showed consistent urinary oxytocin reactivity after the same behavioural contexts. However, East Group males had higher urinary oxytocin levels across contexts than South Group males, including higher baseline levels. Our results support the oxytocinergic system’s involvement in cooperation and gregariousness, and suggest an association between group-specific social dynamics and oxytocinergic profiles.

Across Africa, chimpanzee communities exhibit large behavioural diversity not exclusively explained by ecological or genetic variation. However, excluding subtle environmental factors is difficult when comparing far-apart populations. Taï National Park offers a unique opportunity to explore the impact of social learning on behavioural diversity. The Taï South and Djouroutou communities live only 60 km apart in a continuous ecosystem. However, these groups apply semi-different techniques when nut-cracking. Djouroutou chimpanzees crack five species of nuts, exclusively using stone tools. Taï South only cracks four of those species, using stone and wooden tools, and does not exploit abundant Sacoglottis gabonensis nuts. Moreover, this group uses stone and wooden tools. Here, we compared tool material availability and tool choice. Our results showed that both groups did not differ in available nut trees and access to different materials. The communities responded to these ecological conditions differently than predicted if availability was the only factor responsible for shaping behaviour. This highlights the potential role of cultural behaviour in wild chimpanzee feeding ecology.