Do Adult Male Spider Monkeys (Ateles geoffroyi) Preferentially Handle Male Infants?

Infant tolerance by adult males has been observed in many primate species with multimale-multifemale mating systems, but males do not usually initiate interactions with infants. In male philopatric species, such as spider monkeys, adult males within a community exhibit high levels of cooperation and affiliation, and they might therefore be motivated to create bonds with potential future allies. Based on this hypothesis we predicted that adult male spider monkeys would participate in infant handling more than adult females and they would preferentially direct handling toward male infants. Between January 2008 and July 2010, we collected 884 h of observation on a community of wild spider monkeys at Runaway Creek Nature Reserve in Belize. During this period we observed 120 incidences of affiliative interactions between infants and adults other than their mother. The adult initiated the majority of nonmother adult-infant interactions (78 %). All available infants (5 males, 7 females) were handled during the study. All 9 of the community adult males handled infants but only 7 of 14 adult females did so. Adult males handled infants significantly more often than did adult females and males also handled young infants more often than older infants. Significant infant sex differences in handling appeared in infants >6 mo when adult males handled males significantly more than females. The patterns of infant handling among age-sex class dyads reflect the affiliative social patterns that we see in adult spider monkeys. These results provide support for the hypothesis that adult males preferentially handle male infants as a strategy for fostering social bonds.