Long-term temporal stability of personality in chimpanzees (Pan troglodytes): Comparison of trait ratings and behaviour codings over a quarter of a century

Abstract

There is a lack of research examining whether trait ratings and behaviour codings yield similar measures of personality in nonhuman animals, and whether these measures are stable over the long term. Here, we compare personality assessments in the same group of zoo-housed chimpanzees over a 25 year period, offering a rare opportunity for the analysis of long-term temporal stability of personality in this species. We attempt to disentangle the effects of time and measure through an analysis of similarities and differences at a group and individual level. The first wave of the study rated 59 chimpanzees’ personality traits on an adapted version of the Madingley Questionnaire. The trait principal component analysis (PCA) revealed five components: Submissiveness, Extraversion, Neuroticism, Agreeableness and Openness. A separate PCA identified five components based on behavioural codings: Grooming, Play, Sociability, Aggression and Responsibility. The second wave, with 19 individuals, identified three components arising from behavioural codings: Popularity, Sociability and Influence. When comparing across time for the 11 chimpanzees common to both waves, our primary hypothesis, that trait ratings from the first wave would not correlate with behaviour codings from the second because they are measuring different axes, was largely supported. Our second hypothesis, that the behaviour codings carried out during the two waves would correlate because they were measuring the same thing, was supported, both at the component level and the individual behaviour level, thus providing evidence of stability of behaviour codings over time, particularly those reflecting sociability measures. Personality trait ratings were different to behavioural codings and included aspects not captured through those codings, including intelligence, apprehension, excitability and gentleness; thus, we argue that they represent a more comprehensive characterisation of individuality.