I spent many months in the field, along with many other researchers, trying to figure out what these chimps are up to. So far we have two main theories. The behaviour could be part of a male display, where the loud bang made when a rock hits a hollow tree adds to the impressive nature of a display. This could be especially likely in areas where there are not many trees with large roots that chimps would normally drum on with their powerful hands and feet. If some trees produce an impressive bang, this could accompany or replace feet drumming in a display and trees with particularly good acoustics could become popular spots for revisits.
On the other hand, it could be more symbolic than that – and more reminiscent of our own past. Marking pathways and territories with signposts such as piles of rocks is an important step in human history. Figuring out where chimps' territories are in relation to rock throwing sites could give us insights into whether this is the case here.
Even more intriguing than this, maybe we found the first evidence of chimpanzees creating a kind of shrine that could indicate sacred trees. Indigenous West African people have stone collections at“sacred” trees and such man-made stone collections arecommonly observed across the world and look eerily similar to what we have discovered here.
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