Social Interactions and Proximal Spacing in Woolly Monkeys: Lonely Females Looking for Male Friends

Abstract

Female woolly monkeys usually disperse from natal groups and have been reported to migrate between groups more than once, while male dispersal is less common. This social organization is expected to show a low frequency of affiliative behaviors among females. In this study, we describe social interactions in woolly monkeys and show a case study comparing proximal spacing in three populations (continuous forest: Tinigua and Cueva de los Guacharos National Parks and El Trueno station: 163 ha fragment). We also discuss how social interactions may be affected by fragmentation. We used instantaneous samplings on focal animals to estimate the frequency and overall rates of social interactions, and we estimated social affiliation using frequency of proximity (<5 m). As expected, these populations show a low frequency of adult individuals in proximity, since adult females were rarely close to each other, and proximity among adult males was also very low. We found few differences between populations in the overall frequency of social interactions, but the type of interactions was highly context dependent, since these were strongly affected by the number of estrous females and juveniles present in the groups (which are known to vary strongly along time). Our results show that female dispersal in woolly monkeys yields low levels of affiliation among adult females and that the most common patterns of affiliation correspond to relationships enhancing direct reproductive success (i.e., adult female–offspring and adult male–adult female pairs). We suggest that these patterns of association occur because woolly monkeys have a lower incentive to defend territories than other atelines, due to their common use of scattered feeding sources (i.e., arthropods) and their mating system (including the recurrent migration of females and promiscuous copulations, perhaps in search of male support and protection). These traits allow a wide variety of female interactions that result in cohesive groups or fluid groupings which seem to depend on intra- and interspecific interactions. Our results also suggest that woolly monkeys in fragments show similar social behavior to the one exhibited by populations in pristine forests, at least when resource productivity is relatively high.