Intergroup Transfer of Females and Social Relationships Between Immigrants and Residents in Bonobo (Pan paniscus) Societies

Abstract

This paper first reviews data collected from 1976 to 2013 regarding the life histories of members of the main E1 study group of bonobos (Pan paniscus) in Wamba. The E1 group exhibited strong tendencies toward female dispersal and male residence during the entire study period, thereby exemplifying the typical characteristics of a male-philopatric and female-dispersal society. This pattern did not change after the abandonment of artificial provisioning. We then present two new cases of immigrant females, focusing especially on social association patterns, dominance relationships, and affiliative interactions during the approximate 2.5 years from the time of their immigration to their first birth. These females began engaging in social grooming with resident females immediately after their arrival but rarely did so with adult males, suggesting that they regard social bonding with females as more important than that with males. They also emigrated at a young age and frequently engaged in social play. Indeed, social bonding established through frequent social play may be related to the development of socially symmetrical relationships, which are the basis for the egalitarian bonobo society. Intragroup competition for food and mates was unlikely explanations for the tendency toward female dispersal. However, male residence and the risk of father–daughter incest may encourage female transfer among bonobos.