Courtship and Mating Behavior of Wild Orangutans in Sumatra

Abstract

All field studies describe the orangutan as an animal with a predominantly solitary life style and a low frequency of social interaction. It is not really surprising therefore that, despite all the field work in the past 15 years, literature still provides little factual knowledge about the social behavior and the reproductive behavior of this species. It is especially remarkable that previous field studies contain very few observations of copulations. Copulations by subadult males have been reported by MacKinnon (1974) and Rijksen (1978). Matings by adult males have been seen by Galdikas (1978) and by myself. Between June 1975 and April 1979 I studied a wild orangutan population in Ketambe in the Gunung Leuser Reserve in Sumatra. The study focused on the animals’ social behavior and as part of this study I was extremely lucky to have the opportunity in the field to make an extensive detailed observation of courtship and mating behavior. So far only part of the data has been worked out, so I shall restrict myself in this paper to giving a qualitative account of the courtship and mating behavior.