Male Chimpanzees in Guinea-Bissau Throw Rocks at Trees for Decades

Male chimpanzees in Guinea-Bissau's Boé National Park repeatedly throw rocks at the same individual trees [1, 2].

This behavior suggests the existence of complex cultural traditions in non-human primates, indicating that certain social activities can be passed down through generations regardless of a clear survival utility.

Researchers, including Dr. Catherine Hobaiter and Dr. Michael Huffman, have observed the behavior for more than 10 years ^[2]. Systematic study of the activity began around 2012 and has continued through this week ^[2]. The primates target more than 30 individual trees ^[1], leaving gnarled scars on the bark and creating large accumulations of stones at the base of the trunks.

"The rock-throwing is a form of cultural tradition passed down through generations of males," Hobaiter said ^[2].

The scale of the activity is significant. Dr. Michael Huffman said the piles can reach up to two meters high, creating a striking visual record of the behaviour ^[2]. Local guide Amadu said the chimpanzees return to the same spots year after year ^[2].

Scientists are currently debating the exact purpose of the rock-throwing. Some evidence suggests the behavior is primarily a display of dominance among males ^[2]. Other reports indicate the activity may be used to attract females during the breeding season ^[1]. Because the behavior is consistent across the group, researchers believe it serves as a form of social signaling, though the specific intent remains uncertain [1, 2].

Boé National Park is a savanna-woodland protected area located in the north-east of Guinea-Bissau [1, 2]. The continued study of these populations provides a rare look at how primate cultures evolve in isolated environments.