'Big mama' bonobos help younger females stand up for themselves

"We may have uncovered one of the ways in which females maintain a superior status in bonobo society," says lead author Nahoko Tokuyama of Kyoto University.

In their study, Tokuyama and fellow researcher Takeshi Furuichi observed a group of wild bonobos at Wamba, Democratic Republic of the Congo.

"Primate females sometimes forge partnerships to attack others. Typically, such coalitions are formed between relatives to protect useful resources from non-relatives." says Tokuyama. "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; a major research goal for us was to highlight the dynamics in which coalition-forming happens in non-relative individuals."

Through four years of observation they found that all female coalitions were formed to attack males, usually after males behaved aggressively toward one or more females. They also found that older females have better chances of winning when the battle is one-one-one, and when females form alliances they always win over males. What's more, the older females don't play favorites; whether a younger female is friendlier with the older female has no relation to whether the older female comes to help.

Tokuyama observes that coalition-forming in female bonobos may have evolved as a way to combat male harassment. "Young females have a lower social status than males, but protection from older females seem to let young females join the group without fear of being attacked by males. By controlling aggression by males in this manner, females maintain overall superiority in the social hierarchy.

"It's beneficial for the older females as well, because the younger females start spending more time with them in hopes of getting protection. This way, the older female can give her son more opportunities to mate with the younger females. Such partnerships might in fact be the very factor that fosters gregariousness and promotes tolerance among females."