Over 13 days of observations, another much older female called Chappy, thought to be 34 years old, became repeatedly aggressive toward Kiki, either chasing or physically attacking her on 28 separate occasions. During 19 of these interactions, another orangutan intervened, physically stepping between the two squabbling apes to separate them. Most of the time the peacemaker was an elder female orangutan called Gypsy, who is thought to be 51 years old.
Researchers suspect that the behavior is learned because these orangutans, who are loners in the wild, have been forced to live together. (BBC News, via Boing Boing.)