Ecological risk-taking across age in Barbary macaques

Abstract

When foraging, animals face decisions regarding unpredictable resources and varying predation risk, in which the cost-benefit trade-off must be assessed. Life-history theory focuses on resource allocation with regard to development and suggests there should be a variation in risk-taking propensity across age, manifested by a shift in goals from gain acquisition to loss aversion over time. Consequently, we aimed to assess age-related variation in decision-making strategies under risk in Barbary macaques (Macaca sylvanus) living at "La Foret des Singes" in Rocamadour, France. We experimentally varied the perceived risk and potential gains in a 2x2 design. The high-risk stimulus was a rubber snake; the low-risk stimulus a cube with a snakeskin pattern. The high-value food reward was a peanut; the low-value food reward a popcorn. In 2022, we presented 83 subjects with one of the four possible factor combinations, and in 2023, we presented 70 individuals with the inverted combination (e.g. snake-popcorn in 2022, cube-peanut in 2023). We took each monkeys propensity to retrieve the reward as a measure of risk-taking, and the latency to retrieve the reward as motivation to engage in the risky choice. Regardless of age, subjects generally retrieved the reward when placed next to the cube, whether peanut or popcorn, but were less likely to retrieve the reward placed next to the snake when this was popcorn rather than peanut. However, older individuals were faster than younger conspecifics to retrieve the reward when it was popcorn, whether paired with the cube or snake. Our results do not comply with the notion that risk-taking propensity declines with age, but rather suggest that in this paradigm, the animals assess the costs and benefits of a risky situation across age, and that the subjective value of a resource may change with age.