Anthropological Institute and Museum, University of Zurich
Saturday 2:45-3:00, Grand Ballroom II
Sumatran orangutans (Pongo abelii) show the latest age of first reproduction and longest nutritional dependence of any nonhuman primate. Sumatran orangutans live in a highly skill intense foraging niche including extractive foraging and tool use. In this study on wild Sumatran orangutans at Suaq Balimbing Indonesia, we could show that immatures reach competence in foraging skills well before age of first reproduction: soon after weaning they have reached diet compositions, food processing rates and competence in finding food equal to those of their mothers. Consequently, the late age of first reproduction in Sumatran orangutans cannot be determined by the time to acquire foraging skills but rather by the energetic constraints of reaching adult body size. However, we also found that the slow somatic development provides immatures with a surfeit of time for skill learning: by vertical transmission (expressed in selective peering to, and food sharing with, the mother), by high rates of independent exploration during infancy, and by post-weaning associations with conspecifics. In the latter context, they pay close attention towards close by feeding party members, expressed by high peering rates, consistent with the presence of horizontal transmission of feeding innovations. We compare this pattern of energy limiting the age at first reproduction in orangutans with that seen in human foragers, where adult skill levels are reached well after the onset of reproduction, and propose that provisioning during the learning period allowed our ancestors to evolve an even more skill-intensive foraging niche.