Long-term studies on wild bonobos at Wamba, Luo Scientific Reserve, D. R. congo: Towards the understanding of female life history in a male-philopatric species

Abstract

Long-term studies on wild bonobos began at Wamba, in the current Luo Scientific Reserve, in 1973. Except for several interruptions due to political instability and civil war, we have been conducting studies of identified individual bonobos over 35 years, providing valuable data on their population dynamics and life history. Although the number of groups and number of individuals in the northern section of the reserve decreased by half during the interruptions of the study, the number of members of the main study group has steadily increased since 2002 when we resumed the study. Our long-term data demonstrated the male-philopatric structure of the group. There is no confirmed case of emigration of males from the study group, and no case of immigration of males into the group. On the other hand, all females born into the study group disappeared by the age of 10 years, and females with estimated ages of 6-13 years immigrated into the study group. These ages of intergroup transfer are much earlier than those reported for chimpanzees. Exceptional cases of immigration of two adult males and two adult females with offspring occurred right after the war. It is likely that remnants of extinct groups joined the study group. Such integration of members of foreign groups highlights the peaceful nature of bonobo society. The study group is characterized by an extremely high tendency for female aggregation. Various factors, including high density of food patches, female initiative in ranging, prolonged estrus of females, and high social status of females, seem to be responsible for the high attendance ratio of females in mixed-sex parties. Our long-term observations therefore provided evidence for interesting behavioral contrasts with chimpanzees.