Comparison of personality structures between methodologies: personality ratings and behavioural observations in Japanese macaques (Macaca fuscata)

In this study, we aimed to clarify the structure of personality of Japanese macaques (Macaca fuscata) using two methods, personality ratings and behavioural observation, which are frequently used in primate personality studies. Principal component analysis of personality ratings sampled in two waves that were assessed with questionnaires (Stevenson-Hinde and Zunz questionnaire in Wave 1 and Hominoid Personality Questionnaire in Wave 2) revealed four components for each wave: Dominance, Aggressiveness, Dependency, and Component4 and Dominance, Aggressiveness, Sociability, and Activity. By calculating the correlation coefficients for principal component loadings of personality ratings, we compared the personality structure of other primates from previous studies with that of Japanese macaques. Based on these results, we propose that the factors common to macaques and capuchin monkeys fall into the following four categories of Dominance, which correlates with dominance rank; Excitability, which expresses aggression and neuroticism; Sociability, which indicates how actively they try to interact with others; and Activity, which expresses exploratory behaviour and openness. Analysis of data from behavioural observation extracted four components: Kin-biased-approaching, Grooming-diversity, Activity, and Aggressiveness. Principal component scores were calculated from each rating and behavioural observation data, and correlation coefficients were used to examine whether the same personality traits were found in both these methods. In this analysis, the raters did not collect behavioural data to ensure that data from both these methods did not overlap. No identical personality traits were found between the two methods. This result may indicate that there was no specific personality structure in Japanese macaques and that each method assessed different aspects of behavioural patterns pertaining to animal behaviour. It is difficult to assume from this study the cross-situational consistency conventionally assumed by personality psychology, and the results suggest that individuals vary in the way their behaviour changes in response to their environment, that is, coherence.