Why do male chimpanzees throw rocks at the same trees for more than a decade? We travelled to remote Guinea-Bissau to find out

Accumulative stone throwing is a rare, potentially cultural, behaviour that has been observed among four groups of wild chimpanzees in West Africa. (Wikimedia Commons), CC BY-SA

Walking through the savanna-woodland landscape of Boé National Park, Guinea-Bissau, you might encounter a tree covered in gnarled scars, with an accumulation of rocks surrounding its base.

The chimpanzees may have left the area, but you are lucky nonetheless, because you have stumbled upon evidence of a rare — and potentially cultural — chimpanzee behaviour: accumulative stone throwing.