Acquisition of object-robbing and object/food-bartering behaviours: a culturally maintained token economy in free-ranging long-tailed macaques

Abstract

The token exchange paradigm shows that monkeys and great apes are able to use objects as symbolic tools to request specific food rewards. Such studies provide insights into the cognitive underpinnings of economic behaviour in non-human primates. However, the ecological validity of these laboratory-based experimental situations tends to be limited. Our field research aims to address the need for a more ecologically valid primate model of trading systems in humans. Around the Uluwatu Temple in Bali, Indonesia, a large free-ranging population of long-tailed macaques spontaneously and routinely engage in token-mediated bartering interactions with humans. These interactions occur in two phases: after stealing inedible and more or less valuable objects from humans, the macaques appear to use them as tokens, by returning them to humans in exchange for food. Our field observational and experimental data showed (i) age differences in robbing/bartering success, indicative of experiential learning, and (ii) clear behavioural associations between value-based token possession and quantity or quality of food rewards rejected and accepted by subadult and adult monkeys, suggestive of robbing/bartering payoff maximization and economic decision-making. This population-specific, prevalent, cross-generational, learned and socially influenced practice may be the first example of a culturally maintained token economy in free-ranging animals. This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates'.

Animal Cognition in an Urbanised World

“…Learning may also allow urban-dwelling animals to take advantage of novel foraging opportunities provided by humans. For example, long-tailed macaques (Macaca fascicularis) at the Uluwatu Temple in Bali, Indonesia frequently steal inedible items from visitors, and use these items as bartering tokens in exchange for food rewards, the quality of which are based on the value of the stolen item (Leca et al, 2021). Observational and experimental data suggest that this behaviour is learned, with individuals becoming more successful in their bartering interactions with age (although this may be partly due to noncognitive factors such as physical strength, which influence individuals' ability to steal higher-value items).…”

“…Observational and experimental data suggest that this behaviour is learned, with individuals becoming more successful in their bartering interactions with age (although this may be partly due to noncognitive factors such as physical strength, which influence individuals' ability to steal higher-value items). Older macaques also showed evidence of payoff maximisation by actively seeking more or higher-quality food rewards in exchange for higher-value items (Leca et al, 2021).…”

“…These studies should therefore be carried out on a wide range of taxa, with hypotheses and predictions grounded in the natural history of the species in question. This is particularly important given that studies of urban cognition currently show a strong taxonomic bias toward birds; further studies in other urban invaders, such as foxes, rats, raccoons and primates, are urgently needed (e.g., Daniels et al, 2019;Leca et al, 2021). Moreover, further study is needed within urban populations to explore how and why individuals vary in their cognitive performance.…”

Economic behaviours among non-human primates

“…One of the most obvious examples of an economic organization among monkeys is given by the already quoted above example of the Balinese Uluwatu temple macaques. New data and interpretation are provided by Jean-Baptiste Leca [14] and his colleagues in their paper 'Acquisition of object-robbing and object/food-bartering behaviours: a culturally maintained token economy in free-ranging long-tailed macaques'. This field study will be very satisfying for anyone who is seeking a model-independent demonstration that properly labelled economic behaviours can emerge among non-human primates outside laboratory-stylized experiments.…”

“…Many limitations and wrong conclusions can arise owing to the way an experiment has been designed and run or because the parameters of a model have been mis-specified. Leca et al [14] suggest a different and most convincing ecological validation of an emergent and sustaining primate model of a trading system. If we look closely at its social and material organization, we see that this trading system is not random.…”