But they usually forage alone. Because males and females seem to have rather different ways of 'belonging' to a group, it is probably more correct to refer to the social units simply as 'communities'. The males form the stable backbone of a chimp group, females moving and are freely accepted among groups, although any accompanying offspring may be killed . As a result, females within a group are usually unrelated and not close. Bonobos are even less bound by social ties and comprise mainly of maternal units of a mother and offspring, including grown sons, with males forming bachelor groups.
Hierarchy is based on age and size but also on alliances and friendships.
In such fluid communities, aggressive behaviour is common but seldom result in outright violence. Chimps and bonobos have complex communication methods involving facial expressions, gestures and calls. Grooming is vital in establishing and reinforcing bonds. Chimps are particularly territorial and a stronger encroaching community may systematically kill and drive out an occupying community. She may mate with several males, who show no rivalry for her.