The effects of infant births on male-female relationships in Cebus capucinus.

Most primates are characterized by cohesive male-female bonds that are maintained year round. While recent studies have addressed the selective pressures influencing the evolution of male-female relationships in primates, we know relatively little about the proximate mechanisms affecting them. It has been demonstrated that newborn white-faced capuchins (Cebus capucinus) attract the attention of other group members and this may be an important mechanism influencing male-female relationships. We studied two groups of C. capucinus in the Area de Conservación Guanacaste, Costa Rica, between February and July 2007. A total of 348 hr of focal data were collected on all adult males (n=6) residing in each of the study groups. During our study, 13 of the 14 group females were either pregnant or lactating, and 9 infants were born. We calculated an average daily affiliation rate between all group males combined and each adult female four weeks before and four weeks after the birth of her infant. Repeated measures ANOVAs revealed no significant changes in affiliation following infant births (F=2.262, df=1, P<0.176). Results remained nonsignificant for rank (F=1.550, df=1, P<0.260) and group membership (F=0.729, df=1, P<0.429). Infant sex was the only variable with a significant effect on affiliation rates between males and females (F=10.020, df=1, P<0.019). Adult males increased their affiliation with all adult females that gave birth to male infants (n=4), while their rates decreased with all but one of the adult females with female infants (n=4). While preliminary, these results indicate that the adult males may cultivate relationships with other males at a young age.