Rank and payoff biases influence subject choices in a foraging task among sanctuary chimpanzees (Pan troglodytes)

Social learning is essential to the development of culture in humans, non-human primates, and other cultural species. Transmission biases (social learning strategies), the cognitive processes that guide conscious and subconscious decisions about when and from whom to learn, are a key branch of social learning. Primatological research has primarily explored single biases in isolation, such as chimpanzee bias toward adopting behavior demonstrated by higher-ranking individuals. However, few studies have considered how simultaneous strategies interact when subjects are given a conflicting choice involving two potentially adaptive biases. This study used a token-reward task with 35 sanctuary-housed chimpanzees at Ngamba Island Sanctuary in Uganda to determine whether chimpanzees more frequently adopt behaviors from high- or low-ranking female demonstrators when those behaviors differ in payoff, providing either a preferred pineapple piece (high-payoff) or a less favored carrot piece (low-payoff). Individuals in Group 1 observed a low-ranking demonstrator collecting the high-payoff reward (pineapple) and a high-ranking demonstrator collecting the low-payoff reward (carrot). Chimpanzees in Group 1 did not adopt one behavior significantly more frequently than the other. In Group 2, the demonstrator roles were reversed, and the frequency of high-payoff selection was higher. This suggests that high-payoff behaviors are more likely to propagate when presented by higher-ranking demonstrators. Additionally, adoption of high-payoff behaviors may be constrained by the presence of alternative, lower-payoff behaviors demonstrated by socially preferred individuals. In turn, this may contribute to explanations of why chimpanzee culture is relatively simple compared to that of humans.