Department of Anthropology, Boston University
March 26, 2015 8:30, Grand Ballroom E/F/G
Orangutans are considered unique among apes in terms of their low level of sociality. Originally characterized as solitary, orangutan researchers have revised this designation over time and now typically classify orangutans as semi-solitary with individual based fission-fusion dynamics. Over the course of a year-long study at Gunung Palung National Park on Borneo, 60% of orangutan follows included social events. Many of these involved actively gregarious or affiliative behaviors, suggesting benefits for social grouping for orangutans beyond simply aggregating at food sources or for mating opportunities. Different age-sex classes engaged in different types of social behavior and displayed different patterns in social partner choice, indicating shifting benefits of sociality through different life history stages. Adolescent females were the most social age-sex class, involved in 69% of all social encounters while mothers with dependent offspring were involved in only 19% of social encounters. Flanged males were present for 31% of social events, and unflanged males were involved in 20%. We discuss behavioral flexibility in orangutans as a result of unpredictable food availability in Southeast Asian rainforests along with the demographic and life history factors that modulate social behavior. This study provides a more nuanced picture of orangutan sociality by examining both the ecological context in which social encounters take place and the factors that influence the social behavior of individuals, allowing for a more thorough understanding of the variation in sociality that is observed between orangutan populations.
Funding was provided by the Boston University GRAF, National Science Foundation (#BCS-0936199), US Fish and Wildlife Service (#F12AP00369), National Geographic Society, PCI, Focused on Nature, and Disney Worldwide Conservation Fund