Masturbation is part of the natural behavioral repertoire of primates, with visual sexual stimuli known to trigger this behavior. Here, we report masturbation events triggered by visual sexual stimulus (VSS) in the South American primate Sapajus libidinosus. We observed a multi-male multi-female captive colony of 17 bearded capuchins between January and October 2014. Over this period, we registered 11 copulation events, 68 attempt copulations, and five masturbation events. The same low-ranking male (named Fu) performed all masturbation events. Fu directly looked at other individuals engaged in sexual displays while he masturbated in three events. The masturbation events associated with VSS lasted up to 2 min and 40 s. Our observations show that VSS can trigger masturbation in capuchin monkeys. The low hierarchy rank of the male, and the consequent lack of mating opportunities in the multi-male multi-female recently formed group in captivity, may have prompted the masturbation events.

手淫是灵长类动物自然行为的一部分，已知视觉性刺激会引发这种行为。在这里，我们报告了南美灵长类动物Sapajus libidinosus中由视觉性刺激 (VSS) 引发的手淫事件。我们在 2014 年 1 月至 2014 年 10 月期间观察到一个由 17 只胡须卷尾猴组成的多雄多雌圈养群落。在此期间，我们记录了 11 次交配事件、68 次尝试交配和 5 次自慰事件。同一位低级别男性（名叫Fu）执行了所有自慰活动。符在三个事件中自慰时直接看着其他人进行性展示。与 VSS 相关的手淫事件持续长达 2 分 40 秒。我们的观察表明，VSS 可以引发卷尾猴的自慰。雄性的低等级，以及随之而来的多雄多雌最近在圈养中形成的群体中缺乏交配机会，可能促使了自慰事件。