Chimps in Guinea-Bissau Throw Rocks at Trees for 10+ Years

Deep in Guinea-Bissau's Boé National Park, wild chimpanzees are maintaining a mysterious tradition that could unlock secrets of human evolution.

Researchers from the Great Ape Behaviour Lab recently completed a groundbreaking expedition to document accumulative stone throwing, a rare behavior where male chimps hurl rocks at specific trees while making loud calls. The chimps return to the same scarred trees again and again, creating piles of rocks at their bases.

The team hiked 22 kilometers into savanna woodland to set up camera traps and recording devices. Working with local field assistants Djei Baldé and Balu Séra, they captured video and audio of this elusive behavior that's only been observed in four West African chimp groups.

The findings are remarkable. The same trees first identified years ago are still being used today, meaning individual chimps maintain this tradition for over a decade. When throwing rocks, the chimps often make pant hoots (long-distance calls) and drum on tree buttresses with their hands and feet.

Scientists believe this represents a cultural behavior with communicative or even symbolic meaning. Unlike tool use for getting food like cracking nuts, accumulative stone throwing appears purely social, marking important locations within chimp territory or conveying messages to other group members.

Why This Inspires

This discovery matters beyond understanding chimp society. Because we share evolutionary history with chimpanzees, studying how they use stones in social contexts helps us understand how our own ancestors developed language and culture. These aren't just random actions but potentially meaningful traditions passed down through generations.

The research also highlights the importance of preserving primate cultural heritage. Just like human archaeological sites, these accumulative stone throwing locations represent irreplaceable evidence of primate culture and behavior.

Local communities in Guinea-Bissau are partnering with conservation organizations like Chimbo to protect these chimps and their habitat. The researchers stayed in Béli village, where residents support the work of documenting and understanding their chimpanzee neighbors.

The team is now analyzing their data to determine what social messages the stone throwing conveys, including identifying which chimps throw rocks and who's watching when they do it.

This window into chimp culture shows us that protecting wildlife means preserving not just species but their rich traditions and ways of life too.