A Landscape Archaeological Approach to Accumulative Stone Throwing (AST) in West African Chimpanzees (Pan troglodytes verus)

Abstract

In Boé National Park in Guinea-Bissau, a community of wild Western chimpanzees (Pan troglodytes verus) has been observed engaging in a novel, potentially cultural, behaviour, accumulative stone throwing (AST). Individuals habitually throw rocks at particular trees, making AST a unique instance of primate stone tool use in a non-foraging context. Repeated throws at the same location leave conspicuous sites on the landscape; therefore, a landscape archaeological approach permits the cross-temporal study of AST trees as archaeological sites connected to human- and chimpanzee-created aspects of this shared landscape and consideration of the ways these aspects contribute to the significance of certain places to the chimpanzees. By mapping the distribution of AST sites, I determine how landscape features influence the selection of specific locations for AST. AST sites were analyzed with QGIS, using spatial mapping analysis integrating multiple sources of data including chimpanzee space-use, rock and tree surveys, proximity to rivers, chimpanzee resources, human settlements, and topographical features. The presence of food trees, in particular Ficus exasperata and Parkia biglobosa, has a significant influence on the likelihood of AST site presence. The frequency of indirect signs of chimpanzee activity was also an important predictor, indicating that AST sites are more likely to occur in the territorial core, an area of high chimpanzee use which contains an abundance of nesting sites and reliable food sources. Increasing our understanding of non-human primate behaviour through spatial archaeological approaches can inform archaeological inferences relevant for hominin evolution and the development of cultural behaviours. Given the Critically Endangered status of Western chimpanzees, studying AST may not only expand knowledge about our hominin ancestors, but also provide support for the importance of biological and cultural diversity in chimpanzee populations.