“Intentional” control of sound production found in leaf-clipping display of Mahale chimpanzees

This study reports three observed episodes involving leaf-clipping behavior of wild chimpanzees. In the first episode, an estrous female moved toward the source of a leaf-clipping sound. In the second, an estrous female escaped from a possessive male by intentionally controlling her production of sound. The third episode involved a male producing a leaf-clipping sound and then concealing the act when a dominant male approached. These episodes might suggest that chimpanzees can control the production of the sound intentionally, and understand that other chimpanzees also comprehend the causal relationship between the production of sounds and the occurrence of subsequent events.