Personality in Captive Chimpanzees: Use of a Novel Rating Procedure

We present a new method to assess the personalities of captive chimpanzees (Pan troglodytes). Using individually generated bipolar constructs, experienced observers rated the personalities of chimpanzees on a five-point scale. Each observer chose a subset of his/her own constructs and we performed a separate factor analysis on each set of ratings. The analyses indicate four factors: dominance, sociability, machiavellianism, and anxiety. We propose that this factor structure will be useful in the development of a single rating instrument with which to assess the personalities of captive chimpanzees.     

Social influences on ranging patterns among chimpanzees (Pan troglodytes verus) in the Tai National Park, Cote d'Ivoire

Group size is expected to be an important factor to predicthome-range (HR) size in social animals. In chimpanzees adultmales play an important role in defending the HR against neighbors,and therefore it has been suggested that HR size depends onthe number of adult males. In this long-term study on wild WestAfrican chimpanzees, we analyzed the relative importance ofcommunity size and composition on ranging patterns over a 10-yearperiod, using multivariate statistics. Because community sizedecreased from 51 individuals with 6 adult males in 1992 to22 individuals with only 1 adult male in 2001, we expected adecrease in HR size, which should be better predicted by thenumber of males than by community size. We further investigatedthe effect of fruit availability on monthly HRs over a 4-yearperiod. As predicted, HR size decreased during the first 7 yearsof our study but increased during the last 3 years. Overall,the number of adult males was the best predictor of HR size,whereas fruit availability did not correlate with HR size. HRuse remained stable over the entire study period, with a constantproportion of about 35% of the HR used as core area. High HRand core-area overlap values between different years indicatedstrong site-fidelity. Although the number of males within thecommunity explained the decrease in HR size, the recent increasein size remains unexplained. This finding suggests that otherfactors such as relative fighting power of males affect HR size.     

Peering in mature, captive bonobos (Pan paniscus)

“Peering”—close-proximity staring at the mouth of another—was observed in ten (three males and seven females) mature (at least 7 years old) bonobos (Pan paniscus) living in three social groups at the San Diego Zoo and Wild Animal Park. Instantaneous scan samples, taken at 2-min intervals, over a three-and-a-half year period, yielded 617 observations of peering (1.4 per observation hour). Food was exchanged in only 15 of these scans. Peering was most often performed by younger animals and was primarily directed toward older females (“matrons”). In a given dyad, the animal more likely to peer at the other was also more like to both peer and be peered at if they frequently groomed and infrequently displayed aggression at a given female. An adolescent male showed the highest frequency of peering when living with two older females, but dropped to adult male levels when later housed with two younger (albeit mature) females. A reversal in which animal was more likely to peer, follow, and groom occurred in one female dyad, after the birth of the younger animal's first infant. After a similar birth in the other group, no such changes were observed. We discuss how these and related findings, in conjunction with what is known of the social structure of this species, suggest that one possible function of peering in bonobos may be as a signal acknowledging female status.