Physiological stress hormone levels and mating behaviour are negatively correlated in male rhesus macaques (Macaca mulatta)

In order to understand the factors that cause and mediate stress in social animals, many studies have examined differences in male physiological stress levels between mating and non-mating seasons, and related these differences to levels of male-male competition. Very few have explicitly tested whether variation in stress levels is related to mating behaviour itself. We provide preliminary evidence of a negative relationship between faecal levels of glucocorticoid metabolites and mounting frequency in free-ranging male rhesus macaques (Macaca mulatta). This finding may help explain the previous observation that male rhesus macaques show no difference in their levels of faecal glucocortocoids between the breeding and non-breeding season, despite the former being associated with elevated levels of aggression. Our study highlights the importance of directly quantifying mating behaviour when investigating the potential impact of reproductive competition and seasonality on stress physiology.