Behavior and reproductive endocrinology of male white-faced capuchins (Cebus capucinus) in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica
I examined male endocrinology and social bonds in relation to dominance status in four groups of wild white-faced capuchin monkeys, Cebus capucinus, in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica. I used noninvasive monitoring of male fecal androgen and glucocorticoid levels to examine the hormonal correlates of dominance and rank acquisition. In spite of low rates of aggression among coresident males, alpha males had higher androgen (testosterone and dihydrotestosterone) levels than subordinate males. Among subordinates, adult males had higher androgen levels than subadult males. During a non-aggressive rank increase, the new alpha male’s androgen levels increased immediately after attainment of the alpha position, and continued to increase for several months thereafter, while glucocorticoid increases lagged behind. In contrast, a subordinate adult male in the group had no change in androgen or glucocorticoid levels. Female white-faced capuchins do not display behavioral estrus, and ovulation is not associated with any changes detectable to the human observer. Therefore, I inferred female reproductive status by analyzing fecal progesterone and estradiol. Alpha and subordinate males experienced androgen and glucocorticoid increases in the presence of fertile females, a period likely associated with increased sexual activity and competition among coresident males. Androgens and glucocorticoids were also higher in the dry season, when intergroup encounters were more frequent. High competition between groups may facilitate low rates of intragroup aggression and the formation of social bonds within groups. I found that coresident males formed differentiated social bonds, and formed stronger social bonds when they had fewer coresident males and when group sex ratio was male-biased. Alpha males had the weakest and least equitable bonds, while relationships among subordinate males were characterized by relatively strong and somewhat reciprocal grooming. The importance of male bonds, particularly among subadult males, may reflect the importance of coalitions of immigrant males in the ability to takeover social groups and increase dominance status. A meta-analysis of parallel dispersal – when conspecifics emigrate together or immigrate into groups containing familiar individuals - indicates that in male primates, this behavior may be linked with the propensity of males to form coalitions and the need to retain coalition partners.