On a brighter note, civil strife in Sumatra appears to be ending, and the country is recovering from the 2004 tsunami. This makes it opportune to intensify research and conservation actions with little-studied but very significant wild populations. One of these, with 400-600 individuals, is in a forest area now known as the West Batang Toru Forest Block (WBTFB). Modeling work carried out during a recent Population and Habitat Viability workshop suggests that orangutan populations of 500 or more are demographically and genetically stable in the absence of human-related mortality, habitat loss or unforeseen catastrophic events, and may contribute to the long-term conservation of the species. Populations of 250 have a very high probability of survival under the same conditions, but will be markedly reduced in size and lose substantial genetic diversity.

Of the 13 identified orangutan populations in Sumatra, only seven are estimated at 250 or more individuals and only four at over 500 individuals. This means that the West Batang Toru is one of very few remaining populations with a very high probability of survival under good management. It is also the only potentially viable population wholly within North Sumatra province and, in addition, represents a possibly unique orangutan population on the island, since years of geographical isolation may have led to distinctive genetic and/or cultural traits. Great Ape Trust of Iowa has made a grant to the Sumatran Orangutan Conservation Programme, led by Ian Singleton, to help establish a field station and to conduct a more intensive survey of the population and the threats it faces. This in turn will allow more effective management and protection of the orangutans, and will facilitate conservation-useful research on behavior and ecology.

Web site: www.sumatranorangutan.org