Behavioral style, dominance rank, and urinary cortisol in young chimpanzees (Pan troglodytes)

Remarkable individual variation in primate personalities is evident to those who study them, but the concept of 'personality' has nevertheless received little attention in the nonhuman primate literature. In this study, I introduce a novel implementation of a method to quantify primate personality or behavioral style based on ethological observations and use it to test several predictions about the relationship between personality and dominance rank in young captive chimpanzees living at the New Iberia Research Center in New Iberia. Louisiana. I demonstrate that while some behavioral styles are related to dominance rank (smart, aggressive, playful, and mellow), others are not (affiliative and friendly). Furthermore, dominance rank is a poor predictor of stress as reflected by baseline urinary cortisol levels, but individuals who score highly in the 'smart' behavioral style component show significantly higher cortisol levels than those whose scores in this component are low, perhaps reflecting different stress levels experienced by these two groups. I discuss the implications of these findings and encourage researchers of animal behavior to consider behavioral style an important variable in their study populations, as it may ultimately help us further our understanding of social evolution and life histories.