a1 Great Ape Trust of Iowa, 4200 SE 44th Avenue, Des Moines, IA, 50320, USA.
a2 Orang-utan Conservation Services Program, Balikpapan, Indonesia, and Tropical Forest Initiative, The Nature Conservancy, Balikpapan, East Kalimantan, Indonesia.
a3 Department of Anthropology and Graduate Group in Ecology, University of California, Davis, USA.
a4 Wildlife Research Group, Department of Anatomy, University of Cambridge, UK.
a5 Kinabatangan Orang-Utan Conservation Project, Sandakan, Sabah, Malaysia.
a6 IUCN/SSC Conservation Breeding Specialist Group, Apple Valley, USA.
a7 Anthropological Institute & Museum, University of Zürich, Switzerland.
a8 Fauna & Flora International–Indonesia Programme, Kompleks Pusat Laboratorium UnivNasional, Ragunan, Jakarta, Indonesia.
a9 Yayorin (Yayasan Orang-utan Indonesia), Pangkalan Bun, Central Kalimantan, Indonesia.
a10 UNEP–World Conservation Monitoring Centre, Cambridge, UK.
a11 Conservation International–Indonesia Programme, Jalan Pejaten Barat, Kemang, Jakarta, Indonesia.
a12 Center for International Forestry Research, Bogor, Indonesia.
a13 Wildlife Conservation Society-Malaysia, Kuching, Sarawak, Malaysia.
a14 Harvard University, Department of Anthropology, Peabody Museum, Cambridge, USA.
a15 Sumatran Orang-utan Conservation Programme, Medan, Indonesia.
In recognition of the fact that orang-utans (Pongo spp.) are severely threatened, a meeting of orang-utan experts and conservationists, representatives of national and regional governmental and non-governmental organizations, and other stakeholders, was convened in Jakarta, Indonesia, in January 2004. Prior to this meeting we surveyed all large areas for which orang-utan population status was unknown. Compilation of all survey data produced a comprehensive picture of orang-utan distribution on both Borneo and Sumatra. These results indicate that in 2004 there were c. 6,500 P. abelii remaining on Sumatra and at least 54,000 P. pygmaeus on Borneo. Extrapolating to 2008 on the basis of forest loss on both islands suggests the estimate for Borneo could be 10% too high but that for Sumatra is probably still relatively accurate because forest loss in orang-utan habitat has been low during the conflict in Aceh, where most P. abelii occur. When those population sizes are compared to known historical sizes it is clear that the Sumatran orang-utan is in rapid decline, and unless extraordinary efforts are made soon, it could become the first great ape species to go extinct. In contrast, our results indicate there are more and larger populations of Bornean orang-utans than previously known. Although these revised estimates for Borneo are encouraging, forest loss and associated loss of orang-utans are occurring at an alarming rate, and suggest that recent reductions of Bornean orang-utan populations have been far more severe than previously supposed. Nevertheless, although orang-utans on both islands are under threat, we highlight some reasons for cautious optimism for their long-term conservation.
(Received October 31 2007)
(Reviewed January 22 2008)
(Accepted March 04 2008)
p1 Also at: Department of Conservation Biology, Chicago Zoological Society, Brookfield, USA.