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 behavior in non-human primates. However, the ecological validity of these laboratory-based experimental situations tends to be limited. Research aims to address the need for a more ecologically valid primate model of trading systems in humans.
Macaque monkeys at a Bali temple can spot expensive items to steal and ransom for food. The well-known phrase cheeky monkey has some basis in fact, if a new study on the behavior of the primates is anything to go by. 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. Observational and experimental data showed
- Age differences in robbing/bartering success, indicative of experiential learning
- Clear behavioral associations between value-based token possession and quantity or quality of food rewards rejected and accepted by sub adult 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. Adult wild long-tailed macaque monkeys were intelligent enough to comprehend which items had the highest value to the visitors, such as an electronic item, and would only release it after receiving food they perceived to be of corresponding value. The scientists filmed the monkeys as they stared at a visitor, inconspicuously approached them, took an object, and then stepped aside waiting for a suitable offering.
The adult monkeys accumulated “several food rewards before returning the token” where the item was of high value, and were “more likely” to accept a “less preferred food reward” in exchange for a lower value item, the study said.
This field observational and experimental study of token-robbing and token/reward-bartering interactions in the free-ranging population of Balinese long-tailed macaques produced three main findings:
- These behaviors need to be learned throughout juvenescence (i.e. until up to 4 years in this species) to be successfully performed;
- Older monkeys preferentially selected tokens that were more valued by humans;
- These more skillful and selective individuals appeared to make economic decisions, as evidenced by clear behavioral associations between value-based token possession and quantity or quality of food rewards rejected and accepted.
Sub adult and adult monkeys (but not juveniles yet) have learned to map their token-robbing behaviors onto the hierarchical (and arbitrary) scale of values attributed by humans to different tokens: they preferentially selected tokens that were more likely to be exchanged for food (e.g. electronic devices, pairs of glasses) over other objects that were less valuable for humans and typically not worth bartering (e.g. empty camera bags, hairpins)
The present naturalistic research setting represents a unique opportunity to study field economics and explore macroeconomic phenomena in non-human primates in environmental conditions that are more externally and ecologically valid than those provided by the traditional token exchange paradigm.