In the savanna-forest landscapes of Guinea-Bissau, one can come across a tree with signs of impact and piles of stones at its base. This is not a coincidence or the work of humans: apparently, a rare behavior of western chimpanzees—cumulative stone throwing—has been played out here for decades.
This phenomenon was first documented in 2016 in four populations of Pan troglodytes verus in West Africa. Adult males approach certain trees, emit loud pant-hoot calls, sometimes drum on roots, and hurl or throw stones at the trunk or hollow. As a result, noticeable accumulations of stones form in the same places, and the bark becomes covered with characteristic scars.
Research shows that the behavior is limited to a narrow region and does not depend solely on the availability of stones or suitable trees. This suggests its cultural nature: young individuals learn the tradition from older ones. The sites have remained active for more than ten years—expeditions in 2017 and recent years have confirmed that chimpanzees continue to return to the same trees.
Possible explanations include long-distance communication, displays of strength, or even symbolic marking of territory. Stone throwing is often combined with classic root drumming and probably serves to amplify the signal in an excited state. Unlike tools for obtaining food, here the stone is used in a social context.
Such cultural traditions highlight the complexity of behavior of our closest relatives and their vulnerability to threats. In Guinea-Bissau, chimpanzee habitats are at risk due to bauxite exploration, which could lead to the loss of not only the environment but also unique behavioral practices.
Studying these rituals with camera traps helps to understand how exactly chimpanzees use the sites and how conspecifics react to them, and also reminds us of the need to preserve not only species but also their cultural heritage.
