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

Long-term Changes in Age-Sex Groups of the Captors and Developmental Stages of the Prey in the Red Colobus Hunting Behavior by the Chimpanzees of Mahale, Tanzania

We analyzed the long-term changes in the age-sex of chimpanzee captors and the developmental stages (estimated by body size) of the colobus prey. We also analyzed whether any specific male chimpanzees disproportionately contributed to the red colobus hunting over time. The data were obtained from a 46-year observation at Mahale Mountains National Park, Tanzania. In the early stages of this long-term study, only mature and adolescent male chimpanzees hunted red colobus, and these hunts were mostly single-kill episodes. But over time, mature and adolescent female chimpanzees began to participate in red colobus hunts as well, and the number of multiple-kill episodes increased. The developmental stages of the red colobus taken as prey also diversified over time. In particular, the rate of infant prey increased, which suggests that chimpanzees may have developed hunting tactics to counter the antipredator tactics of female colobus that have dependent offspring. Thus, the spread of red colobus hunting appears to have increased the diversity of the age-sex classes of chimpanzees acting as hunters and the range of developmental stages of red colobus taken as prey. No consistent tendency was observed that specific male chimpanzees contributed in red colobus hunting more than others continuously over the years. Nevertheless, male chimpanzees tended to kill the red colobus more frequently when they had the alpha status