Chimpanzees have been hurling rocks at the same trees for more than a decade

Some chimpanzees in West Africa repeatedly throw rocks at particular trees, creating piles of stones that can remain in use for more than a decade. Researchers think this unusual behavior may be cultural and could serve as a form of communication, territorial signaling, or something more symbolic. Camera traps and audio recordings are now being used to reveal who throws the stones and how nearby chimpanzees respond.

Chimpanzees have been hurling rocks at the same trees for more than a decade. The chimpanzees may have left the area, but you are lucky nonetheless, because you have stumbled upon evidence of a rare — and potentially cultural — chimpanzee behavior: accumulative stone throwing. Video recordings show wild western chimpanzees, usually adult males, throwing rocks at specific trees and repeatedly returning to these trees to perform the behavior.

[See video link after end of article.] While throwing, the chimpanzees pant hoot — a loud, long-distance communicative signal — and sometimes repeatedly hit their hands and feet on the tree in a behavior called buttress drumming. We have just returned from a field site in Guinea-Bissau where we collected data to help us investigate the social and ecological context of accumulative stone throwing to determine what these chimpanzees are trying to communicate. Given our evolutionary relatedness to chimpanzees, we hope accumulative stone throwing can help us understand the emergence of complex communication and stone tool use over the course of human evolution.