Male social bonds: strength and quality among co-resident white-faced capuchin monkeys (Cebus capucinus)

Social relationships among immigrant same-sex co-residents have received relatively little attention, particularly for species where males are the dispersing sex. White-faced capuchins (Cebus capucinus) are unusual in that immigrant males form cooperative alliances with co-resident males during intergroup encounters, and also have affiliative and tolerant intragroup relationships. We collected approx. 3341 h of focal animal data on 25 adult and subadult males in five groups of wild Cebus capucinus in the Santa Rosa Sector, Costa Rica, across three distinct field seasons. Using generalized linear mixed models, we examined the influence of number of co-resident males, group socionomic sex ratio, dominance status and age, and past parallel dispersal on social bond strength (i.e., proximity, contact rest, grooming, preferred grooming partners) and quality (i.e., grooming reciprocity) for 47 unique male male dyads. Overall, dyads that included an alpha male had the weakest and least equitable bonds, while dyads composed of subordinate males had the strongest and most equitable bonds, with subordinate subadult peers being most likely to form preferred relationships. Several measures of bond strength and quality were highest among dyads in groups with few males and low socionomic sex (female-to-male) ratios. Dyad partners who had previously engaged in parallel dispersal had slightly better bonds than those that did not, suggesting that kinship and/or familiarity may be important. Our results indicate that within groups, male relationships are influenced by power asymmetry, partner availability, and dyad relationship history.