Leadership of old females in collective departures in wild bonobos (Pan paniscus) at Wamba

Abstract

Group-living animals need to coordinate their activity in order to maintain gregariousness. Although individuals have their own nutritional, social, and reproductive needs, they have to reach consensus to decide where and when to travel. Collective movements are the outcome of one individual’s departure, who is then followed by other group members. We investigated departure initiation in a group of bonobos at Wamba, DR Congo, to determine the distribution of leadership among group members. If three or more bonobos started moving more than 30 m, we assigned the individual who moved first as the one who initiated the movement. Two hundred and fifty-four departures were observed. First, we examined whether the frequency of initiation differed according to the following attributes of individuals: sex, age, stage in sexual swelling cycle, dominance, and affiliative relationship. We also examined whether one or more individual(s) initiate departure more or less frequently than expected by chance. A significant interaction between sex and age was found, indicating that the effect of age was greater among females than among males. Individuals who were more central to the grooming network initiated departures more frequently. The three oldest females initiated more often than expected. Old females may be followed because of coalitionary supports they often give to younger females, and of their greater knowledge about ranging area. Leadership in bonobos was not equally shared among group members, and old females were “key individuals” who helped to maintain cohesiveness in their fission-fusion society. When group-living animals travel from one location to another, they must coordinate when and where to travel; otherwise, they might spread apart. Bonobos are one of our closest living relatives and have a fission-fusion social system. We investigated the initiation of group departure in wild bonobos to determine the distribution of leadership among group members. We found that the frequency of initiation was associated with the individual’s age, affiliative relationships, and male dominance rank. The three oldest females initiated departures more frequently than expected, suggesting that these individuals were habitual initiators and took an important role to preserve cohesiveness. We discuss how this “old female leadership” may emerge in a male-philopatric society.