Corat Clara, Siqueira José, Ottoni Eduardo B
Department of Experimental Psychology, Institute of Psychology, University of São Paulo, São Paulo, SP, 05508-030, Brazil.
Av. das Nações Unidas, 8341, Apto 82B, São Paulo, SP, 05425-070, Brazil.
Primates. 2016 Jan;57(1):113-21. doi: 10.1007/s10329-015-0491-1. Epub 2015 Sep 28.
Stone-aided nut-cracking requires the coordination of three elements: the agent must assemble nuts, a "hammer" stone and an "anvil." Under naturalistic settings, nut-cracking sites, constituted of anvil-like surfaces and already containing a hammer stone, can be fairly stable, lasting as long as the "hammer" stays in place. In an experiment with a semi-free-ranging group of tufted capuchin monkeys (Sapajus sp.) we observed the behavioral sequences leading to nut-cracking. We positioned nuts, hammer, and anvil at the vertices of a 10-m-sided equilateral triangle. Thus, to crack a nut the individuals had to visit the vertices and gather the movable elements (nut and hammer) at the anvil. Under such conditions, the monkeys systematically employed a nut-hammer-anvil vertex visit sequence, one of the shortest and more cost-effective possible routes. In the following experiment, we examined whether the gathering of the hammer after the nuts resulted solely from a "nut first" strategy or if the monkeys were also minimizing hammer transport costs. We positioned two hammers, of the same weight, at different distances from the nuts and anvil, so the cost of hammer transportation (energy and risk of injury) would be higher or lower depending on the choice of hammer (the hammer closer to the nuts being farther from the anvil). We found that, instead of collecting the closest hammer, after collecting the nut, the monkeys systematically chose the hammer closer to (and beyond) the anvil, thus minimizing transport costs.
主体必须集齐坚果、一块“锤子”石头和一块“砧座”。在自然环境中，由类似砧座的表面构成且已经有一块锤子石头的坚果砸开地点可能相当稳定，只要“锤子”保持在原位就能持续存在。在一项对一群半放养的簇绒卷尾猴（Sapajus sp.）进行的实验中，我们观察了导致坚果砸开的行为序列。我们将坚果、锤子和砧座放置在一个边长为10米的等边三角形的顶点处。因此，为了砸开坚果，个体必须前往各个顶点，并在砧座处集齐可移动的元素（坚果和锤子）。在这种情况下，猴子们系统地采用了坚果 - 锤子 - 砧座顶点访问顺序，这是可能的最短且最具成本效益的路线之一。在接下来的实验中，我们研究了在收集坚果后收集锤子是否仅仅是由于“先收集坚果”的策略，或者猴子们是否也在尽量减少锤子的运输成本。我们放置了两把重量相同的锤子，它们与坚果和砧座的距离不同，所以锤子运输的成本（能量和受伤风险）会根据所选择的锤子而更高或更低（离坚果较近的锤子离砧座较远）。我们发现，在收集坚果后，猴子们不是收集最近的锤子，而是系统地选择离砧座较近（且更远）的锤子，从而将运输成本降至最低。
