Longitudinal changes in the targets of chimpanzee (Pan troglodytes) hunts at Mahale Mountains National Park: how and why did they begin to intensively hunt red colobus (Piliocolobus rufomitratus) in the 1980s?

The hunting activities of chimpanzees (Pan troglodytes) at Mahale Mountains National Park exhibited a significant change over a 46-year observation period, shifting from sporadic hunting for small ungulates and primates through seizure or chasing, to a specialized hunting habit for red colobus (Piliocolobus rufomitratus). By the early 1980s, a new hunting habit had developed through the following stages: (1) occasional single kills by mature/adolescent males, (2) multiple kills by mature/adolescent males, (3) participation of mature females in both multiple and single kills, and (4) increased frequencies of multiple kills and female participation in killing. Throughout the observation period, red colobus was the most frequently hunted species, accounting for 71.0% of all hunts, 68.1% of all kills, and 70.3% of the consumed prey. Adult/adolescent female chimpanzees accounted for 23.1% of all kills and 20.4% of red colobus kills, both of which are higher than proportions reported in other areas. There are several possible explanations for these changes: (1) improved observation conditions, including familiarization of the chimpanzees with human observers; (2) environmental changes such as forest and faunal recovery, particularly an increase in the red colobus population; (3) change(s) in observation methods; (4) a new invention or (5) reinvention by the Mimikire (M) group chimpanzees; and (6) the change in intergroup relationships between the M and Kajabala (K) groups.