Selecting nest-sites of sumatran organ-utans,Pongo pygmaeus abelii in the Gunung Leuser National Park, Indonesia

Abstract

In the Gunung Leuser National Park of Indonesia a population of orang-utans has been observed. The location of 172 night-nest sites has been examined with respect to their position in relation to the last food tree visited during the preceding day and with respect to their height above the ground. There were significant differences between the sex-age classes in the distribution of distances between nest-sites and the last visited food tree. The more vulnerable animals nested at greater distances and also tended to nest at greater height. These aspects of nest-sites selection have been interpreted in terms of an anti-predator strategy: the more vulnerable animals avoid nesting in fruit trees; instead they prefer more cryptic, unpredictable and inaccessible sites.