Laboratory of Human Evolution Studies, Graduate School of Science, Kyoto University, Kyoto, Japan.
Am J Primatol. 2020 Jun;82(6):e23130. doi: 10.1002/ajp.23130. Epub 2020 Apr 15.
Extractive foraging is considered a key selective pressure for the evolution of primate cognitive abilities-the extractive foraging hypothesis. Although tool-use and substrate-use are representatives of the foraging strategy, some primates engage in extractive foraging without external objects. Manual processing skills of prickly foods have been described in some species, whereas there are few studies on other type of food defenses. Here, I describe extractive foraging of hard-shelled walnuts by wild Japanese macaques (Macaca fuscata), focusing on whether they accomplish the tasks only by their physical strength or require manual and/or oral processing skills to crack open the walnut shells. The study subjects comprised all members of troop B and three nontroop males in Kinkazan Island, Japan. Walnut feeding was observed during the main walnut seasons (September-December) when the troop visited walnut patches for 79 days in 2 years. I categorized the walnut feeding behavior into complete cracking and partial cracking. The number of times the five behavioral elements in the cracking stage occurred were counted from complete cracking. All six adult males and 11 of the 17 adult/adolescent females showed complete cracking, while the remaining females were never observed exhibiting this activity, despite their physical maturity. I observed four clearly distinguishable cracking methods during walnut feeding in the 17 subjects. The compositions of five behavioral elements were different in each method. These results suggest that walnut feeding by Japanese macaques is not only by brute force but requires the acquisition of at least one of four cracking methods for the achievement of complete cracking. In particular, females need to compensate for their physical inferiority by increasing walnut manipulations. To my knowledge, this is the first detailed description on feeding techniques in primates to overcome hard-shelled obstacles without the use of tools and even substrates.
采集觅食被认为是灵长类动物认知能力进化的关键选择压力——采集觅食假说。虽然工具使用和基质使用是觅食策略的代表，但有些灵长类动物在没有外部物体的情况下进行采集觅食。一些物种已经描述了对多刺食物的手动加工技能，而关于其他类型的食物防御的研究很少。在这里，我描述了野生日本猕猴（Macaca fuscata）对硬壳核桃的采集觅食行为，重点关注它们是否仅通过自身力量完成任务，还是需要手动和/或口腔加工技能来敲开核桃壳。研究对象包括日本琴平岛上 B 群的所有成员和 3 只非群内雄性。在 2 年内，当该群体在主要的核桃季节（9 月至 12 月）访问核桃地时，观察到了核桃喂养行为。我将核桃喂养行为分为完全破裂和部分破裂。从完全破裂中计算出破裂阶段的五个行为元素的发生次数。所有 6 只成年雄性和 17 只成年/青少年雌性中有 11 只表现出完全破裂，而其余雌性尽管身体成熟，但从未观察到这种行为。我在 17 个研究对象中观察到了四种在核桃喂养期间明显不同的破裂方法。这四种方法的五个行为元素的组成不同。这些结果表明，日本猕猴的核桃喂养不仅是靠蛮力，还需要至少掌握四种破裂方法中的一种才能完成完全破裂。特别是，雌性需要通过增加核桃操作来弥补自身的体力劣势。据我所知，这是第一个关于灵长类动物在没有使用工具甚至基质的情况下克服硬壳障碍的进食技术的详细描述。
