| dc.description.abstract | Nest construction is a daily habit of independent orangutans for sleeping or resting. Data on their nests
have been used in various ecological studies (e.g., density estimation, ranging behavior, evolution of
material culture) because they are the most observable field signs. We investigated nest size and nest
site features of Bornean orangutans in the wild during 10 months’ fieldwork at three sites in East
Kalimantan, Indonesia: Kutai National Park, Birawa, and Meratus. To examine individual variation,
we followed 31 individual orangutans and recorded the 92 nests they made for nest size (diameter) and
nest site features (height of nest above ground, tree species used for the nest site, the diameter and
height of the tree, whether the nest was new or reused, and nest location within the tree). Analyses
taking age–sex classes of the focal individuals into consideration showed significant age–sex differences
in nest size and location, but not in nest height or nest tree features (diameter, height of tree, and
height of lowest branch). Mature orangutans (adult females, unflanged and flanged males) made larger
nests than immatures (juveniles and adolescents). Flanged male orangutans with larger nests used
stable locations for nesting sites and reused old nests more frequently than immatures. The overall
proportion of nests in open (exposed) locations was higher than in closed (sheltered) locations. Flanged
males and immatures frequently made open nests, whereas adult females with an infant preferred
closed locations. The good correspondence between nest size and age–sex classes indicates that nest size
variation may reflect body size and therefore age–sex variation in the population. | en_US |
