Permana, A.; Permana, J. J.; Nellissen, L.; Prayogi, E. S.; Prasetyo, D.; Wich, S. A.; van Schaik, C. P.; Schuppli, C.

Immature great apes learn how to build their nests over multiple years, yet how they do so has remained largely unclear. We investigated the detailed role of social learning in the acquisition of nest-building skills in wild Sumatran orangutans (Pongo abelii) using data on nest-building, nest practice, and nest peering behaviour from 44 individuals, collected over 17 years. We found that nest peering (but not being close to a nesting individual without peering) is associated with a significant increase in nest practice behaviour, and mostly directed at multi-step nest elements. Dependent immatures mostly peer at their mothers and use nest tree species in common with her, independent immatures peer at a larger range of individuals and use nest tree species in common with them. Our results suggest that orangutans acquire their nest-building skills through observational social learning including selective attention to \"know-how\" and the transmission of \"know-what\" information.