“I Want to Mate?” or “I'm Afraid?”

The scientists also proposed several other examples of chimpanzee culture, including an activity known as leaf clipping. In this behavior, a chimp gathers one to five stiff leaves and bites bits of the leaves off without eating them. The biting produces a distinctive ripping sound. This behavior was first observed in the chimpanzees of the Mahale mountains in Tanzania, and the scientists eventually witnessed it at six of the seven study sites—all except Gombe. However, leaf clipping seems to be done for different reasons by different groups.

At Mahale, young male and female chimpanzees clip leaves to attract each other's attention. The behavior and the sound it produces have a meaning that might be translated as, “I want to mate.” But at Bossou, the same leaf-clipping behavior has an entirely different meaning. The researchers working there found that chimpanzees engaged in leaf clipping when they were startled by the observers. Over time, as the chimpanzees became accustomed to the presence of the scientists, they stopped leaf clipping. At Tai, leaf clipping appears to be practiced only by male chimps who also drum on trees with their hands. The males engage in both activities as a means of asserting themselves.