Visual communication by chimpanzees (Pan troglodytes): effects of rearing history on gestures and visual orienting behaviors

This study was designed to examine rearing history differences in gestures and visual orienting behaviors by chimpanzees. We administered two conditions to 101 chimpanzees: In the visible condition, a banana was visible to both the chimpanzee and a human observer; in the hidden condition, the observer did not know and the subject did know in which of two buckets a banana had been hidden. Rearing history did not influence either the propensity to gesture or the type of gesture exhibited. To assess visual orienting behavior, we recorded the durations, in seconds, that each chimpanzee looked at (a) the observer, (b) a baited bucket, (c) an unbaited bucket, and (d) elsewhere; there were 44 subjects whose gaze was captured on film in both conditions. Subjects apportioned most of their visual fixation toward the experimenter in both visible and hidden conditions (F(3,123) = 30.30, p < .001). Nursery-reared subjects discriminated between the visible and hidden conditions in the apportionment of their visual orienting behavior, whereas neither mother-reared subjects or those who were wild-born did so (F(2,18) = 4.83, p = .021). Looking more at the baited bucket in the hidden condition was significantly associated with whether the observer selected the baited bucket (Spearman's r(N = 42) = .303, p = .026, one-tailed). Differences in early rearing history are associated with subtle differences in looking behavior in captive chimpanzees.