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

<b>Abstract</b><br/><p>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 lab-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 (1) age differences in robbing/bartering success, indicative of experiential learning, and (2) clear behavioral 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.</p>

<b>摘要</b><br/>&lt;p&gt;代币交换范式（token exchange paradigm）研究表明，猴类与类人猿能够利用物体作为符号性工具，以换取特定的食物奖励。此类研究为解析非人类灵长类动物经济行为的认知基础提供了重要视角。但这类基于实验室的实验情境往往生态效度（ecological validity）有限。本野外研究旨在填补这一空白，开发一种生态效度更高的、用于研究人类交易系统的非人灵长类动物模型。在印度尼西亚巴厘岛乌卢瓦图神庙周边，有一个规模庞大的自由活动长尾猕猴种群，它们会自发且规律性地与人类开展代币介导的以物易物互动。这类互动分为两个阶段：猕猴先从人类手中窃取不可食用但价值各异的物品，随后将这些物品作为代币返还给人类，以此换取食物。我们的野外观测与实验数据显示：（1）窃取/以物易物的成功率存在年龄差异，这表明该行为存在经验学习过程；（2）亚成年与成年猕猴基于价值的代币持有量，与其拒绝或接受的食物奖励的数量、质量存在明确的行为关联，这暗示猕猴会通过窃取/以物易物实现收益最大化，并开展经济决策。这种具有种群特异性、广泛传播、跨代传承、经学习且受社会影响的行为模式，可能是野生自由活动动物中首个由文化维系的代币经济（token economy）实例。&lt;/p&gt;