Mating behaviour of male orangutans in the Kutai Game Reserve,Indonesia

The mating behaviour of male orangutans was investigated during a 16-month field study at the Kutai Game Reserve, Indonesia. Males competed for access to mates during interactions involving females. The highest-ranking male in the study population consistently displaced lower-ranking adult and subadult males when females were present. Adult males regularly supplanted subadults during similar interactions. Both adult and subadult males forcibly copulated with females. Subadult males, however, achieved more matings than adult males by copulating frequently during prolonged associations with females. Adult males mated with a few females within a defined area, or searched for mating opportunities with more females over larger regions. In this and other studies, individual male reproductive success could not be determined, and therefore remains a critical area for future research.