KOTA KINABALU, MALAYSIA--The orangutan, our closest relative after chimpanzees and gorillas, only lives in the lowland rainforests of Borneo and Sumatra, in Indonesia and Malaysia. Although orangutans probably numbered over 300,000 a century ago, scientists in 1997 estimated only 36,000 to remain, due to poaching, habitat loss, and fire. New and improved census data, presented at an international workshop on these apes here earlier this month, suggest this depressing trend has continued. At the same time they hint at the ape's resilience.
A problem with the earlier estimates, says orangutan researcher Sri Suci Utami Atmoko of Universitat Nasional in Jakarta, Indonesia, was that they relied on aerial photographs of patches of suitable orangutan habitat (ScienceNOW, 11 May 2000). To check if the apes were actually there, she and other researchers visited forests in Sumatra and looked for the animals or signs of their presence, such as the sleeping nests they fashion each night high up in trees. The results were disappointing. Many of the populations near Lake Toba that were thought to exist in the late 1990s had vanished, she says, adding that some may not have been there to begin with. She estimates that the Sumatran population, which consisted of more than 12,000 orangutans in 1997, has almost halved since then.
At the same time, good news comes from the other end of the simian's range. In the 1950s, some researchers estimated that 50,000 orangutans still lived in the vast forests of North Borneo. These forests have since fallen prey to severe logging, so that by 1997, just 1700 orangutans were thought to remain. That estimate turns out to be too pessimistic, according to primatologist Marc Ancrenaz of the French conservation organization HUTAN. Over the past 2 years, Ancrenaz and collaborators from the Sabah Wildlife Department used ground and helicopter surveys to count sleeping nests in all major forests in Sabah, the Malaysian state that includes North Borneo. After having walked 325 and flown 2000 kilometers, they arrived at an estimate of close to 13,000 individuals. Pooled with the survey data from Sumatra and elsewhere in Borneo, the researchers think that over 30,000 orangutans still exist in the wild.
The new censuses are "more refined" than earlier ones, says zoologist Junaidi Payne of WWF-Malaysia, who surveyed orangutan populations in Borneo in the 1980s. More importantly, he points out, the Sabah study shows that orangutans can thrive in forest that is heavily damaged by logging.
Related site
The Orangutan
Network
Orangutan information from the WWF
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