'Grass-in-the-ear' technique sets new trend in chimp etiquette: Chimpanzees spontaneously copy arbitrary behavior

In 2010, van Leeuwen first noticed how a female chimp named Julie repeatedly put a stiff, strawlike blade of grass for no apparent reason in one or both of her ears. She left it there even when she was grooming, playing or resting in Zambia's Chimfunshi Wildlife Orphanage Trust sanctuary. On subsequent visits, van Leeuwen saw that other chimpanzees in her group had started to do the same.

This aroused his interest to find out if they copied what Julie did by watching and learning from her through so-called social learning. The research team, including Zambians who monitor the chimpanzees daily, collected and analyzed 740 hours of footage that had been shot during the course of a year of 94 chimpanzees living in four different social groups in the sanctuary. Only two of these groups could see one another.

The research team found that only one of the four groups regularly performed this so-called "grass-in-the-ear" behavior. In one other group one chimpanzee once did the same. Eight of the twelve chimpanzees in Julie's group repeatedly did so. The first to copy her was her son, Jack, followed by Kathy, Miracle and Val with whom she regularly interacted. Generally at least two of the chimps put grass in their ear at the same time. Interestingly, the chimpanzees Kathy and Val kept up the custom even after Julie, the original inventor of this behavior, died.

The observations show that there's nothing random about individual chimpanzees sticking grass into their ears. They spontaneously copied the arbitrary behavior from a group member. Chimpanzees have a tendency to learn from one another -- clearly a case of "monkey see, monkey do" in fact. Van Leeuwen suggests that those animals that find a specific behavior somehow rewarding will continue to do so on their own, even if the chimpanzee they have learned it from is no longer around.

"This reflects chimpanzees' proclivity to actively investigate and learn from group members' behaviors in order to obtain biologically relevant information," says van Leeuwen. "The fact that these behaviors can be arbitrary and outlast the originator speaks to the cultural potential of chimpanzees."