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.