Abstract
Mating activity of a wild Mueller’s gibbon group (Hylobates muelleri) was observed in the Danum
Valley Conservation Area, Sabah, Malaysia. The purpose of this study was to investigate the function of copulation calls in
gibbons. The female emitted copulation calls at the time of intromission and pelvic thrusting. Copulation calls were composed of
two notes and one of them was sung only while mating. Approximately half of copulation calls were sung near the range boundary.
Mating with copulation calls sometimes occurred while singing. According to the model that female copulation calls have evolved
under the selective pressures of risk of infanticide and sperm competition, copulation calls should be rare in species with little
female promiscuity. As gibbons usually live in pair-living social organization and have a monogamous mating system, no vocal
signals by female gibbons are considered to be needed. However, clear copulation calls were emitted by the female. It suggests
that the relationship between paired gibbons is unstable. Copulation calls by the female Mueller’s gibbon may function to increase
mate guarding and strengthen the pair bond.
Social Organization and Mating System of Macaca Fascicularis (Long Tailed Macaques)
