Bonobos have a reputation as the hippies of the primate world, with a make-love-not-war image. But scientists appear to have underestimated their bloodthirsty tendencies. In a new study, researchers report observing wild bonobos hunting and eating monkeys, which shows that the apes are not so different from their more aggressive cousins, the common chimpanzees.
Ever since researchers recognized bonobos (Pan paniscus) as a different species from common chimpanzees (Pan troglodytes) 75 years ago, they have noticed fundamental differences between the two apes. Male common chimpanzees form gangs that hunt monkeys, dominate female chimpanzees, and even murder other males in territorial skirmishes. By contrast, bonobo males spend more time having sex, are pushed around by females, and have even been observed grooming monkeys. One explanation for the difference is that bonobo males are kept in check by females, which form tight alliances that prevent males from dominating them and forming macho hunting parties necessary to capture elusive monkeys. Researchers thought that bonobos hunted only prey such as forest antelopes and squirrels that were easy for an individual to capture.
But far less is known about bonobos than about common chimpanzees, because there are so few bonobos left in the wild. Only between 5000 and 60,000 remain in the lowland forests of the Democratic Republic of the Congo, where regional conflicts have made it difficult for researchers to get an accurate picture of their behavior.
Six years ago, behavioral ecologist Gottfried Hohmann of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues began observing a group of more than 30 bonobos in the Salonga National Park. By last fall, they had habituated the bonobos to humans so they could observe them closely--a process that took longer than usual because poachers had killed apes in the park. On 15 April, Hohmann's graduate student, Martin Surbeck, called to tell him that he had seen four females and one juvenile male bonobo rush up a tree to ambush a group of redtail monkeys, snatch one, and eat it. That was just the beginning, the researchers report in today's issue of Current Biology. Between April and June, Hohmann and his field crew observed six hunting expeditions in which male and female bonobos killed and ate monkeys--and many failed attempts.
This hunting blurs a key distinction between bonobos and common chimpanzees. "It shows that bonobos have coordinated hunts, which until now was reported only for chimpanzees," says primatologist Frans de Waal of Emory University in Atlanta. It also suggests that monkey hunting in apes is very ancient, dating back to the common ancestor of chimpanzees and humans. But bonobo males seem to hunt monkeys less often than do common chimpanzee males, which suggests that bonobo males have lost some of the aggression that is abundant in common chimpanzees, says Harvard University primatologist Richard Wrangham.
Females may be responsible. Unlike in common chimps, among whom males do all the hunting and control access to the kills, "females are hunting and the females are sharing most of the meat" in bonobos, says Hohmann. "I think female dominance drives how often males hunt." Because male bonobos can't monopolize the meat--or use it to curry favor with females--they may not have the same incentive as male chimpanzees to hunt as often.