18.02.2020 - 15:07
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Department of Primatology

Max Planck Institute for Evolutionary Anthropology
Deutscher Platz 6
04103 Leipzig

phone: +49 (0)341 3550 - 200
fax: +49 (0)341 3550 - 299

Giulia Sirianni

Max Planck Institute for Evolutionary Anthropology
Department of Primatology
Deutscher Platz 6
D-04103 Leipzig, Germany

phone: +49 341 3550 249
e-mail: giulia_sirianni@[>>> Please remove the brackets! <<<]eva.mpg.de

Cognitive and Energetic implications of Nut Cracking

Tool use may embed some causal understanding of functionally relevant properties of the physical world. Therefore, selection of tools for a given task, represents a suitable model to test causal cognitive abilities.

Chimpanzees from the Taï forest habitually crack open Coula edulis nuts using stone and wooden hammers. Coula nuts represent a large fraction of their energetic intake for about 5 months per year.

Selection of the appropriate tool in terms of different physical properties (e.g. weight, hardness) and a smart control of the force during the hit sequence (the nut has to be opened but not smashed) may strongly impact nut-cracking performance and thus the ability to exploit an essential energetic resource.


Current research

The aim of my project is to investigate:

  1. modes of hammer selection, both in an experimental setting and in natural conditions
  2. influences of hammers’ physical properties on different measures of nut-cracking efficiency
  3. patterns in hammering sequences

Our field-experiments, natural observations as well as kinematic analyses of hammering movements are expected to provide novel insights on the optimization of nut-cracking by wild chimpanzees as a manifestation of this species’ physical cognitive abilities.


A typical experimental session

Hammer stolen and multiple function of the same tool

The experimental section of my research project consists in the setting up of field-lab sites in areas of Coula cracking within the home-range of a chimpanzee group. Each lab site consists of a natural anvil, which is provided with nuts and hammers of different physical properties (size, weight, hardness) that we aim to test. A remote video-camera trap is placed at each lab site in order to record occurrences of tool selection and nut-cracking in the absence of a human observer.

The work is sponsored by: