As a part of Max Planck Institute for Evolutionary Anthropology's 'Pan African Programme: The Cultured Chimpanzee,' the West African chimps were filmed placing and throwing rocks at the foot of a tree and also filling gaps in the tree.
Experts have stated that there is no reason why they should be doing this, potentially meaning that it is the beginning of ritual behaviour.
After discovering conspicuous piles of stones next to trees at four research sites in West Africa, the field teams placed camera traps next to them. For instance, at the site of the Chimbo Foundation in Guinea Bissau some impressive videos were recorded which confirmed the researchers' suspicion that chimpanzees were responsible for these stone piles and were regularly visiting these trees.
The PanAf cameras filmed individual chimpanzees picking up stones from beside or inside trees and then throwing those at these trees while emitting a long-distance pant hoot vocalization, says Ammie Kalan.
Importantly, the behavior results in accumulations of rocks at these locations. Whereas it is mainly the adult males practicing this behavior in the context of ritualized displays, some camera traps also revealed females or juveniles doing it. The behavior has only been observed in West Africa and appears to be independent of any foraging context, in which the majority of tool-use behaviors were previously described in chimpanzees.
"This study reports a new chimpanzee behavior not known previously and highlights the potential of the PanAf project to uncover unknown facets of the life of chimpanzees, our closest living relative, said researcher Christophe Boesch, adding "As the stone accumulation behavior does not seem to be linked to either the abundance of stones or the availability of suitable trees in an area, it is likely that it has some cultural elements."
Chimpanzees are often used as a model for the evolution of early hominins. Due to the conspicuous accumulations of stones associated with this newly discovered behavior, it raises questions regarding the interpretation of stone accumulation sites in archaeology. Intriguingly, the authors also suggest that this behavior could shed some light on the origin of ritual sites in hominin evolution.
The study appears in Scientific Reports.
First Published: 07 Mar 2016 06:41 AM