Reflections in the rainforest: full-length mirrors facilitate behavioral observations of unhabituated, wild chimpanzees

We describe behaviors of unhabituated wild chimpanzees in Gabon during repeated encounters with large mirrors installed permanently in their home range. Movement in proximity to the mirrors triggered video cameras that recorded the scene. Data are presented for 51 mirror encounters spanning a 3-year period. After initial wariness, mirror-directed aggressive behaviors were common, especially in adult males, but aggression gradually diminished and eventually almost completely ceased. Focusing on the two mirrors that elicited most reactions, the percentage of chimpanzees showing tension or anxiety also decreased across encounters. These mirrors elicited a range of socio-sexual behaviors interpreted as having a reassurance function, especially when group-level tension appeared high. Chimpanzees also occasionally directed these behaviors towards their own reflection. Despite increasing habituation and positive attraction to the mirrors, none of the chimpanzees displayed signs of self-recognition. We conclude that a combination of large mirrors and video traps can provide valuable information about unhabituated, semi-terrestrial primates in their natural habitat, by inducing the primates to stay in one place for longer than they might otherwise do.