PLoS ONE 7(7): e41044

Do Chimpanzees Use Weight to Select Hammer Tools?

Cornelia Schrauf, Josep Call, Koki Fuwa, Satoshi Hirata

A chimpanzee using a cuboid-shaped hammer to crack open a nut in a pit of the anvil.
Figure 1. A chimpanzee using a cuboid-shaped hammer to crack open a nut in a pit of the anvil.
A chimpanzee using a spherical hammer to crack open a nut in a pit of the anvil
Figure 4. A chimpanzee using a spherical hammer to crack open a nut in a pit of the anvil.
Abstract

The extent to which tool-using animals take into account relevant task parameters is poorly understood. Nut cracking is one of the most complex forms of tool use, the choice of an adequate hammer being a critical aspect in success. Several properties make a hammer suitable for nut cracking, with weight being a key factor in determining the impact of a strike; in general, the greater the weight the fewer strikes required. This study experimentally investigated whether chimpanzees are able to encode the relevance of weight as a property of hammers to crack open nuts. By presenting chimpanzees with three hammers that differed solely in weight, we assessed their ability to relate the weight of the different tools with their effectiveness and thus select the most effective one(s). Our results show that chimpanzees use weight alone in selecting tools to crack open nuts and that experience clearly affects the subjects’ attentiveness to the tool properties that are relevant for the task at hand. Chimpanzees can encode the requirements that a nut-cracking tool should meet (in terms of weight) to be effective.

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Schrauf C, Call J, Fuwa K, Hirata S (2012) Do Chimpanzees Use Weight to Select Hammer Tools? PLoS ONE 7(7): e41044 , doi: 10.1371/journal.pone.0041044