RESUMO
We surveyed Bornean white-bearded gibbon, Hylobates albibarbis, population densities in lowland and hill dipterocarp forests within the Sari Bumi Kusama and Suka Jaya Makmur logging concessions. These surveys were conducted from 20 to 30 March 2018 in Sari Bumi Kusuma areas and 14 to 24 April 2018 in Suka Jaya Makmur. We used a fixed-point count method to detect and plot morning song bouts of gibbon groups at systematically placed listening posts. At each location in Sari Bumi Kusuma and Suka Jaya Makmur, 18 listening posts were established, and 2 observers noted and plotted gibbon morning great calls. Gibbon group density was higher at Suka Jaya Makmur than at Sari Bumi Kusuma; we estimated that there were 2.29 groups per square kilometre in the former area and 1.86 groups/km2 in the latter. Since Bornean white-bearded gibbons are strictly protected by the Government of Indonesia and listed as an Endangered species by the International Union for Conservation of Nature (IUCN), we need better management practices to protect the populations of this species within production forests (outside protected areas).
