AFFILIATION PATTERNS AMONG MALE COSTA-RICAN SQUIRREL-MONKEYS

Remarkably close male bonding exists among Costa Rican squirrel monkeys, Saimiri oerstedi. In this population males were philopatric, exhibited no male-male within-troop aggression, and only very slight evidence for a dominance hierarchy. Juvenile, young and full adult males were spatially clumped in same-age male cohorts. A less intense, secondary association was also shown between the young and full adult male cohorts. These associations were most dense over a spatial scale of 5 m or less, but can also be detected in a 5-10 m distance from a focal male. Males also cooperated in 1) sexual investigation of females during the mating season, 2) aggressive interactions with males of neighboring troops, and 3) valiant defense of infants and subadults from potential predators. In contrast, the spatial association among adult females never exceeded random expectations and only a transitory period of cooperation was observed among mothers during the birth season. Furthermore, there was little evidence of bonds between the sexes. Seasonal variation in affiliation patterns was best explained by fluctuations in food availability and, secondarily, reproductive activity. These results are surprising both from the perspective of the general pattern of male affiliation among primates and the often marked aggression and dominance relationships among males documented in captive and wild populations of South American squirrel monkeys. The ultimate explanation is suggested to be the disparate distribution of fruit resources exploited by South and Central American squirrel monkeys, mediated by effects on female affiliation and dispersal patterns.