Why do chimpanzees throw stones at trees?

Newly discovered stone tool-use behaviour and accumulation sites in wild chimpanzees reminiscent to human cairns

Date: March 3, 2016

Source: Max-Planck-Gesellschaft

Newly discovered stone tool-use behavior and accumulation sites in wild chimpanzees are reminiscent to human cairns, report researchers. Chimpanzees are proficient tool-users, using sticks to fish for termites, to dip for ants, to extract honey, and even using stone or wooden hammers to crack open nuts. Outside the foraging context male chimpanzees sometimes throw branches and stones during displays, or leaf-clip to solicit sex from females. This research has therefore been fundamental for providing insights into natural chimpanzee behavior and most importantly into the differences between populations.

Chimpanzees often use tools to extract or consume food. Which tools they choose for which purpose, however, can differ depending on the region where they live. Researchers of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have thus initiated the 'Pan African Programme: The Cultured Chimpanzee' and, since 2010, have collected data on chimpanzee behavior, demography and resource availability across Africa following a standardized protocol. This is how the researchers encountered a thus far unknown behavior: In West Africa chimpanzees throw stones at trees resulting in conspicuous accumulations at these sites. Why exactly the animals do this the researchers do not yet know, yet the behavior appears to have some cultural elements.

Chimpanzees have been studied for almost 60 years at a few long-term field sites, which are mainly located in East and West Africa. They are proficient tool-users, using sticks to fish for termites, to dip for ants, to extract honey, and even using stone or wooden hammers to crack open nuts. Outside the foraging context male chimpanzees sometimes throw branches and stones during displays, or leaf-clip to solicit sex from females. This research has therefore been fundamental for providing insights into natural chimpanzee behavior and most importantly into the differences between populations. However, at the same time it has also become clear that chimpanzee behavior observed at such a small number of sites is unlikely to be representative of other chimpanzee populations.

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