Population status of the Bornean orang-utan (Pongo pygmaeus) in the Sebangau peat swamp forest, Central Kalimantan, Indonesia

A survey of the density and population size of Bornean orang-utan (Pongo pygmaeus) was carried out in 1995 and 1996 in an area of peat swamp forest in the Sungai (River) Sebangau catchment, Central Kalimantan, Indonesia. Densities were calculated for four forest sub-types by counts of orang-utan sleeping platforms (nests) along line transects. Densities were found to be highest in the tall interior and mixed swamp forest sub-types. Low pole forest supported the lowest density. Habitat disturbance caused by logging was shown to affect orang-utan density within mixed swamp forest. The orang-utan population for a larger peat covered landscape unit (9200 km(2)), including the Sebangau catchment, was estimated to be between 5671 (+/-955) and 8951 (+/-1509) individuals, based upon the area of each forest type, the level of disturbance in each area and corrected to prevent overestimates. This study identifies the presence of a very large, self-sustaining orang-utan population in this region and emphasises the urgent requirement for greater protection of Kalimantan's peat swamp forests in the light of recent and rapid habitat degradation. (C) 2002 Elsevier Science Ltd. All rights reserved.