Photo credit: © Pascal Martin / Fotolia

When a male bonobo harasses a young female, he’d better look out. A coalition of protective older females might be headed his way.

Researchers observing wild bonobos over four years in the Democratic Republic of Congo found that whenever females formed coalitions, they would invariably attack males. This was typically in response to a male displaying aggressive behavior towards another female.

In their study, published in the journal Animal Behaviour, the researchers conclude that “coalitions in female bonobos might have evolved as a counterstrategy against male harassment.”

Alliances feature prominently in the social lives of primates. Often forming among female relatives, these partnerships can strengthen the females’ ability cope with competition from non-relatives.

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Bonobos are unusual in that females typically form alliances with unrelated females. As lead author Nahoko Tokuyama of Kyoto University explains in a press release, "For bonobos, females leave their birth group during adolescence, so females in a group are generally non-relative to each other. Despite this, they frequently form coalitions.”

Females had a better chance of defeating offending males when they formed coalitions than when they confronted a male alone.

The researchers believe that forming coalitions to combat aggressive males has enabled female bonobos to acquire the more dominant position in the social hierarchy. “We may have uncovered one of the ways in which females maintain a superior status in bonobo society," says Tokuyama.

Older females may gain additional value from participating in coalitions. "It's beneficial for the older females as well, because the younger females start spending more time with them in hopes of getting protection,” he explains. “This way, the older female can give her son more opportunities to mate with the younger females.”

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