While the adults expertly open nuts with their hammers and anvils, the young chimps pick up pieces of fruit, crumbling pieces of termite mounds or rotten branches and go about pounding on nuts. It was first seen in chimpanzees of the Mahale Mountains in eastern Africa, about 100 miles from Gombe, and in another region called Bossou in Guinea. Researchers have only seen the Gombe chimps engage in leaf clipping on two rare occasions. To leaf clip, a chimpanzee gathers one to five stiff leaves and bites little bits off with its front teeth without eating the leaves. The biting produces a distinctive ripping sound, which appears to be the goal.
Males drum on trees and make noise by leaf clipping as means of asserting themselves.
When primatologists first began observing chimpanzees at Bossou, they noticed that startled chimpanzees would start shredding leaves. But after the chimps became accustomed to the observers, they stopped. But Galef and the handful of remaining critics of animal culture argue that these behaviors are due to environmental pressures. After all, such pressures lie at the heart of natural selection. Ruling out environmental causes of differences was, in fact, key to the inclusion of any of the behaviors in the Nature paper.