Chimpanzees have been hurling rocks at the same trees for more than a decade

Walking through the savanna-woodland landscape of Bo 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 behavior: accumulative stone throwing.

Video recordings show wild western chimpanzees, usually adult males, throwing rocks at specific trees and repeatedly returning to these trees to perform the behavior .

While throwing, the chimpanzees pant hoot - a loud, long-distance communicative signal - and sometimes repeatedly hit their hands and feet on the tree in a behavior called buttress drumming .

We have just returned from a field site in Guinea-Bissau where we collected data to help us investigate the social and ecological context of accumulative stone throwing to determine what these chimpanzees are trying to communicate.