Negotiated male takeover without infanticide in wild Diana monkeys (Cercopithecus diana)

Male tenure in one-male, multi-female primate systems is inherently unstable, with resident males regularly challenged by outsider males. Takeovers often carry substantial costs for females and infants, including infanticide, yet most existing reports characterize these events retrospectively, from post-hoc changes in group composition rather than continuous observation. We provide a detailed, fine-grained account of a male takeover in a wild group of Diana monkeys (Cercopithecus diana) in Taï National Park, Ivory Coast, tracking vocal activity, male-female proximity, and close-range social interactions from the arrival of an extra-group male (‘Gba’) through the resident male's (‘Pahi’) disappearance and a post-conflict phase. Gba called roughly twice as often as Pahi throughout the takeover, and while Pahi initially responded to female alarm calls far longer than Gba, this pattern reversed over time as Gba's increased and Pahi's declined. Aggression was concentrated almost entirely on male-male interactions, with no agonism directed at females or infants. Female proceptive behaviour and copulation with Gba preceded Pahi's departure earlier that day. No infanticide occurred despite the presence of unweaned infants. Post-takeover interactions between Gba and females increased in frequency and duration and were predominantly affiliative. These findings depict a gradual, negotiated transition rather than an abrupt, violently contested replacement, and represent the first detailed process-level documentation of a peaceful, non-infanticidal takeover in guenons. Our results suggest that female behaviour can actively shape the timing and character of male turnover, challenging assumptions that females in this system have little impact on reproductive transitions.