Determinants of Affiliative Interactions between Adult Males and Lactating Females in Pigtail Macaques (Macaca nemestrina nemestrina)


D. Maestripieri, Committee on Human Development, University of Chicago, 5730 S. Woodlawn Avenue, Chicago, IL 60637, USA. E-mail: dario@ccp.uchicago. edu


In some species of Cercopithecine primates, unrelated adult males and females maintain affiliative relationships (‘friendships’) that are apparently unrelated to mating or parental care. This study investigated the occurrence of friendships in a captive group of pigtail macaques, and some of their possible determinants. Study subjects were six adult males and 15 adult females with their newborn infants. Females were focally observed for 2 h every week during the first 12 wk of lactation. With the exception of the fourth-ranking male, adult males showed little interest in initiating affiliative interactions with lactating females and their infants. Most episodes of contact and grooming were initiated by high-ranking females and directed to the alpha male. Because female grooming was not generally reciprocated by the alpha male, it is likely that females benefited from associating with him in terms of agonistic support or protection. Genetic data on paternity determination indicated that the fourth-ranking male, who displayed high levels of affiliation towards mother-infant dyads, sired most of the infants born in the group in the year prior to this study. Thus, whereas females may be interested in associating with males to obtain their support, some males may affiliate with females as a consequence of their previous mating relationships with them or to increase the chances of future mating success. Taken together, however, the findings of this study provide little evidence that adult males and lactating females maintain strong reciprocal bonds that may qualify as friendships.