Some chimpanzees in West Africa have been hurling rocks at the same trees for more than a decade, leaving behind piles of stones that researchers believe may represent a cultural tradition passed down within the community. The behavior, observed at multiple sites, appears to be deliberate and repeated, with certain trees accumulating large collections of rocks over time.
Scientists studying the phenomenon say the stone-throwing may serve several possible purposes, including communication between groups, territorial signaling, or even a symbolic act whose meaning is not yet fully understood. The behavior is unusual because it is not linked to foraging, hunting, or tool use for food acquisition, which are the more commonly documented reasons for chimpanzee object manipulation.
To better understand the practice, researchers have deployed camera traps and audio recording devices at the sites. These tools are now providing detailed data on which individuals throw the stones, how often the behavior occurs, and how nearby chimpanzees react when a rock is launched. Preliminary observations suggest that the act may draw attention from other group members, supporting the idea that it functions as a form of communication.
The findings add to a growing body of evidence that chimpanzee behavior varies significantly between communities, a pattern often described as cultural. While many animal species show regional differences in behavior, the persistence of this stone-throwing tradition over more than a decade suggests it is being maintained and transmitted across generations rather than arising spontaneously.
Researchers note that the behavior is not observed in all chimpanzee populations, which further points to a cultural origin rather than an innate or environmentally determined trait. The specific trees targeted also appear to be chosen consistently, with some showing signs of long-term use, including worn bark and accumulated rock piles at their bases.
The study raises broader questions about the cognitive and social capacities of chimpanzees, particularly their ability to develop and sustain traditions that serve no obvious survival function. Understanding such behaviors may also offer insight into the evolutionary origins of human symbolic communication and ritualistic practices.
Ongoing monitoring will be needed to determine whether the behavior spreads to other groups or changes over time. The research team plans to continue collecting data from the camera traps and audio recordings to map the full scope of the activity and its social context within the chimpanzee community.
