Inter-Unit Group Transfer of an Immature Male of the Common Chimpanzees and His Social Interactions in the Non-Natal Group

In the Mahale Mountains National Park, Tanzania, a mother-son pair of the common chimpanzee transferred from K group to the neighboring M group. This inter-group transfer resulted from the decrease of the male members of K. The male immigrant of 5-year-old had varied relations with the M group members of each age-sex class. He mated with estrous females, played with adolescents and juveniles, though had few interactions with non-estrous females. In particular, while he was away from his mother for 10 days, he unilaterally followed the adult males of M group, though his younger brother who had been born in this group was killed and eaten by them. The present case clarifies two characteristics of common chimpanzee society, the strong tie between mother and son and the attractiveness of adult males for immature males