Primates' Food Preferences Predict Their Food Choices Even Under Uncertain Conditions

Primates’ food preferences are typically assessed under conditions of certainty. To increase ecological validity, and to explore primates’ decision making from a comparative perspective, we tested three primate species (Pan troglodytes, Gorilla gorilla gorilla, Macaca fuscata) (N = 18) in two food-preference tests that created different conditions of uncertainty. In the first, we showed subjects pairs of photographs of six foods in a randomized manner within each session, so subjects could not predict the next pairing and had to respond in accordance with their preferences. We found individual differences in subjects’ preference and differences in six subjects’ preferences when comparing their selections in this test to selections made when trials were blocked by food pairing (tested previously: Huskisson et al., 2020). In in each trial of the second test we paired the food stimuli with a ‘chance’ symbol, representing a random reward of one of the six foods. Across species, each subject’s propensity to select chance over the known food varied by food type: when the known option was highly preferred, subjects were less likely to select the chance symbol. Additionally, 61.11% of the subjects’ rates of selecting foods in the first test showed a positive trend with the rates of selecting the same foods under conditions of uncertainty here; three of these subjects’ selection rates were significantly correlated between tests. Finally, if the food chimpanzees received for selecting the chance symbol was a preferred food, they were more likely to select chance again in the subsequent trial.