Chimpanzees' Stone-Throwing Ritual Puzzles Scientists

Wild western chimpanzees in Guinea-Bissau exhibit a puzzling behavior known as accumulative stone throwing (AST), where they repeatedly hurl rocks at specific trees. This practice, observed for over a decade, is concentrated in four West African populations and may represent a unique behavioral tradition passed down through generations.

Researchers are investigating this phenomenon, noting that AST sites can remain active for more than ten years, suggesting social transmission of information. The behavior is often accompanied by loud pant-hoots and rhythmic strikes against tree trunks, known as buttress drumming, which are associated with male chimpanzee displays.

Scientists have deployed video and audio recording equipment at these sites in Guinea-Bissau's remote Boé region to gather data. The goal is to identify the age and sex of the chimpanzees involved and understand the social context, potentially revealing if the trees serve as communication markers or symbolic sites.

This behavior is significant as it differs from tool use for food, potentially offering insights into the evolution of complex communication and symbolic behavior in primates. However, this unique cultural heritage is threatened by extractive industries like bauxite mining, which endanger chimpanzee habitat and the persistence of AST sites.