Pay-off-biased social learning underlies the diffusion of novel extractive foraging traditions in a wild primate

Abstract

The type and variety of learning strategies used by individuals to acquire behaviours in the wild are poorly understood, despite the presence of behavioural traditions in diverse taxa. Social learning strategies such as conformity can be broadly adaptive, but may also retard the spread of adaptive innovations. Strategies like pay-off-biased learning, by contrast, are effective at diffusing new behaviour but may perform poorly when adaptive behaviour is common. We present a field experiment in a wild primate, Cebus capucinus, that introduced a novel food item and documented the innovation and diffusion of successful extraction techniques. We develop a multilevel, Bayesian statistical analysis that allows us to quantify individual-level evidence for different social and individual learning strategies. We find that pay-off-biased and age-biased social learning are primarily responsible for the diffusion of new techniques. We find no evidence of conformity; instead rare techniques receive slightly increased attention. We also find substantial and important variation in individual learning strategies that is patterned by age, with younger individuals being more influenced by both social information and their own individual experience. The aggregate cultural dynamics in turn depend upon the variation in learning strategies and the age structure of the wild population.

Keywords: Cebus; behavioural traditions; cultural transmission; extractive foraging; pay-off bias; social learning.

Figure 1.

Adult male NP exhibits the canine seam technique. (Online version in colour.)

Figure 2.

Techniques observed during experiment. Rows are unique individuals, from the oldest (top) to the youngest (bottom). The x-axis represents the sequential order of experimental days. Each colour/shape represents most common technique used by an individual on that day; no point indicates days of no processing. The most successful technique indicated by red triangles (canine seam) diffused to older members of the population. Younger individuals did not use canine seam.

Figure 3.

Posterior predictions of probabilities of choosing a socially observed option with pay-off log(t_open)⁻¹ = 0.5, relative to an observed option that was not successfully opened.

Figure 4.

Relationships between age and (a) attraction to new experience (ϕ) and (b) influence of social information (γ). Black line represents the posterior mean. Solid points are posterior means of individual varying effects. Lighter lines are 100 posterior samples. (Online version in colour.)