National Research Council, Institute of Cognitive Sciences and Technologies, Rome, Italy.
Dipartimento di Biologia e Biotecnologie "Charles Darwin", Università di Roma Sapienza, Rome, Italy.
Am J Primatol. 2021 Jan;83(1):e23221. doi: 10.1002/ajp.23221. Epub 2020 Dec 10.
Tool use in humans can be optional, that is, the same person can use different tools or no tool to achieve a given goal. Strategies to reach the same goal may differ across individuals and cultures and at the intra-individual level. This is the first experimental study at the intra-individual level on the optional use of a tool in wild nonhuman primates. We investigated optional tool use by wild bearded capuchins (Sapajus libidinosus) of Fazenda Boa Vista (FBV; Piauí, Brazil). These monkeys habitually succeed in cracking open the mesocarp of dry cashew nuts (Anacardium spp.) by pounding them with stones and/or by biting. We assessed whether availability of a stone and resistance of the nut affected capuchins' choice to pound or to bite the nuts and their rates of success. Sixteen capuchins (1-16 years) received small and large dry cashew nuts by an anvil together with a stone (Stone condition) or without a stone (No-Stone condition). In the Stone conditions, subjects used it to crack the nut in 89.1% (large nuts) and 90.1% (small nut) of the trials. Nut size significantly affected the number of strikes used to open it. Availability of the stone significantly increased the average percent of success. In the No-Stone conditions, monkeys searched for and used other percussors to crack the nuts in 54% of trials. In all conditions, age affects percentage of success and number of strikes to reach success. We argue that exclusive use of stones in other sites may be due to the higher abundance of stones at these sites compared with FBV. Since capuchins opened cashews with a tool 1-2 years earlier than they succeed at cracking more resistant palm nuts, we suggest that success at opening cashew nuts with percussors may support the monkeys' persistent efforts to crack palm nuts.
人类使用工具可以是可选的，也就是说，同一个人可以使用不同的工具或不使用工具来达到给定的目标。达到相同目标的策略可能因个体和文化而异，也可能因个体内部的差异而不同。这是在野生非人类灵长类动物个体内部水平上首次对工具的可选使用进行的实验研究。我们研究了法萨那多维斯塔农场（FBV；巴西皮奥伊州）的野生卷尾猴（Sapajus libidinosus）对工具的可选使用。这些猴子习惯用石头砸或咬来打开干腰果的中果皮（腰果属），从而成功地打开这些坚果。我们评估了石头的可用性和坚果的阻力是否影响卷尾猴选择砸或咬坚果，以及它们的成功率。16 只卷尾猴（1-16 岁）通过砧木接受了小和大的干腰果，同时还提供了一块石头（有石头条件）或没有石头（无石头条件）。在有石头的条件下，在 89.1%（大坚果）和 90.1%（小坚果）的试验中，实验对象使用石头来砸开坚果。坚果的大小显著影响打开坚果所需的敲击次数。石头的可用性显著提高了平均成功率。在无石头的条件下，猴子在 54%的试验中寻找并使用其他敲击器来打开坚果。在所有条件下，年龄都影响成功率和达到成功所需的敲击次数。我们认为，在其他地点，猴子只使用石头可能是因为这些地点的石头比 FBV 更丰富。由于卷尾猴使用工具打开腰果的时间比它们成功打开更难抵抗的棕榈坚果早 1-2 年，我们认为，使用敲击器打开腰果的成功可能支持猴子持续努力打开棕榈坚果。
