Male emigration and female transfer in wild mountain gorilla

Abstract

IN many group-living primates, males leave their natal group and transfer to other groups far more commonly than do females (for example, refs 1–4). For only one species—the chimpanzee—is there good evidence that females leave their natal group and transfer more commonly than do males^5,6, but little information has been available on the movements in and out of gorilla groups. The structure of the gorilla population in the Virunga Volcanoes of Zaire and Rwanda^7,8 and elsewhere⁹ indicates that males at least leave their natal group: there are a number of lone males; and many groups contain only one fully adult male, but a number of adult females. Schaller⁹ implied that males transferred between groups more often than did females. The few data in ref. 10 indicate, however, that only females transfer between groups, although both males and females leave groups. Incorporating data for 8.5 yr from the Karisoke Research Centre in the Virunga Volcanoes (ref. 10 and unpublished results), this paper provides the first extensive evidence that both male and female gorillas leave their natal group, although some sons may remain; that males that leave initially travel alone; and that only females transfer.