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Five-year study suggests chimpanzees strike stones against trees as form of communication

A recent study by behavioral biologists from Wageningen University & Research and the German Primate Research Center has uncovered a remarkable phenomenon among wild chimpanzees in West Africa: the use of stones to produce sound, presumably as a form of communication.

Over the course of a five-year field study, the research team collected video footage at five distinct locations within a nature reserve in Guinea-Bissau. This was made possible through the use of camera traps and with essential support from local field guides. In specific areas, a striking behavioral pattern was observed: adult male chimpanzees repeatedly struck stones against tree trunks, resulting in characteristic piles of stones at the base of these trees.

The study is in the journal Biology Letters.

Lead author Sem van Loon refers to this behavior as "stone-assisted drumming." "It appears to be related to the classic drumming with hands or feet on hollow buttress roots, which chimpanzees use to convey information over long distances or to display dominance," she explains.

Yet there are clear differences: prior to throwing stones, the animals are more likely to emit loud pant-hoots, followed by silence—an opposite pattern to traditional drumming, where silence typically precedes the noise.

Van Loon suspects a different motivation behind this behavior. "It may be that these loud, low-frequency sounds are meant to carry further than typical within-group communication," she suggests. "The acoustic properties of a stone striking a tree make that feasible in densely forested areas."

The observations point to cultural transmission. Young chimpanzees adopt the behavior from older group members, indicating that it is learned socially rather than genetically inherited.

Marc Naguib, Professor of Behavioral Ecology, underscores the broader significance of the discovery: "It illustrates that culture is not unique to humans and that such behaviors need to be considered also in nature conservation."