Acquisition of object-robbing and object/food-bartering behaviours: a culturally maintained token economy in free-ranging long-tailed macaques
Token economies can run without trainers when the swap is clear and fair.
01Research in Context
What this study did
Scientists watched wild long-tailed macaques in Bali. The monkeys grab objects from tourists and trade them back for food.
The team wrote down every trade for eight months. They noted the monkey’s age and what each swap was worth.
What they found
The monkeys built their own token economy. Older animals traded better and picked higher-value snacks.
Skills grew with age, not with human training. The troop kept the system going without any lab set-up.
How this fits with other research
Weiss et al. (2001) first showed lab monkeys prefer slots that return tokens. Leca et al. move that idea outside cages and prove it can run on its own.
Cowie et al. (2016) argue stimulus control, not the food itself, drives choice. The Bali monkeys back this view: they work for plastic bottles because the swap cue is reliable.
Festinger et al. (1996) used tokens to help a sick child sit through dialysis. Same tool, new setting—wild macaques trade for fun instead of for health.
Why it matters
You now have proof that token economies do not need tight staff control. If wild monkeys keep a market alive, your learners can too. Start small: let a client trade a chip for five minutes of screen time and step back. Watch the system take care of itself.
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02At a glance
03Original 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'.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2021 · doi:10.1098/rstb.2019.0677