As so often is the case when a dire situation causes concerned people to investigate more completely, a reassessment of the new information leads to a surprise finding. Moreover that finding becomes something of a mixed blessing. Such is the case with our current understanding of the total number of wild orangutans in the world. There now appears to be more than we collectively thought several years ago. That is good news. The bad news is that the forces behind the threats to the species, mainly greedy destroyers of habitat, are still at work causing a declining population. The confusing part is that we may have been off the numbers by 300-400%. How could that be?


For over a decade, orangutan conservationists as well as this writer have been telling the world the orangutan population has been falling to levels below 15-25,000 individuals. The numbers in Sumatra were low, some 5-7,000 with the remaining 10-20,000 in Borneo. These numbers were initially derived from field experts at a Population and Habitat Viability Assessment (PHVA) workshop held in Medan, Sumatra in 1993. Survey work was conducted by several teams of investigators. The great fires of 1997 and an increase in the level of forest clearing and conversion, as evidenced by satellite data, gave great cause to everyone involved in the conservation of the species.

As a consequence of this concern, a number of population biologists and wildlife conservation scientists have been in the field conducting the most up-to-date nest counts. These counts are still the best way to assess the population of orangutans, though they are based on a set of assumptions and not direct observation of the orangutan. It is presumed that an individual or mother and offspring build a new nest each night. Based on the decomposition rate of a nest and the number seen along a transect, an estimated density of animals can be derived. Over the past few years, the discovery of a "new" population in Central Kalimantan in the Belantikan watershed at the foothills of the Schwaner Range occurred. Furthermore, a comprehensive survey of Tanjung Puting National Park was conducted in 2003 for the first time.

When a PHVA originally planned for 2003 was rescheduled for January 2004, the latest survey numbers were brought together. Low and behold, it looks as if there are approximately 50-60,000 orangutans under threat today, not the 15-25,000 previously cited. Most of the increase comes as a result of comprehensive surveys in Central Kalimantan mentioned above as well as a convincing case of large populations in Sabah, Malaysia. Central Kalimantan lived up to its billing as being the orangutan capital of the world with approximately half of all orangutan numbers in the province. The Tanjung Puting estimate was reported at 6,000 following forest surveys in 2003. These are numbers that the experts feel confident about. However, there is concern that these numbers might be misconstrued by the public. Therefore, little has been said by the team of experts until recently. Many were concerned the public may not consider there is a real problem to the species and the population is increasing - not declining. If this were so, perhaps many would believe that conservation efforts are paying off, and the species is saved.

Nothing could be farther from the truth. Habitat continues to be degraded or destroyed. Satellite and aerial data and ground-based surveys confirm this. Hunting and poaching still takes place, and orangutan populations are suffering, particularly in Sumatra where the situation is extremely desperate. Orangutan population figures were not upgraded for Sumatra with only 7,500 orangutans estimated from recent surveys. So we need to accept the fact that there were considerably more Bornean orangutans in the past. Obviously, they were poorly underestimated. While some experts claim they have known this all along, they were not willing to go against the majority opinion rendered during the 1990's. Yet, based on the number of orphan apes currently recovered by the handful of rescue organizations, we know that thousands of orangutans have perished over the past decade. We also know that orphan orangutans in villages around Borneo exist in numbers greater than what can be cared for properly at the few rehabilitation/reintroduction centers in Indonesian Borneo. The problems facing orangutan survival still exist. Actually, the numbers are not improving.

The PHVA (August 2004) is now online for anyone to download in Adobe Acrobat format to see the effort of experts from the field and others that put their heads together for nearly a week. The large report is located at:

It is filled with data including the estimated population sizes for the Sumatran species and the three Bornean subspecies, the habitat still available, as well as threats facing the forest and the species. Population numbers are found in various tables and might be confusing if one didn't spend some time seeing how the data were partitioned. Early in the report (page 18), the table lists the population sizes by habitat units or viable populations that seem to represent orangutan taxon (species and Bornean subspecies) as well as special factors. Those numbers total over 44,000 individuals. But when all the populations in Sumatra, Kalimantan (East, Central, and West) (Indonesia), Sarawak and Sabah (Malaysia) are added up, they total much higher: from 50-60,000 individuals.

Of equal interest are the results of a computer model (VORTEX) that simulates population fate scenarios for a species under different threat and habitat conditions. Driven by life history parameters such as sex ratios and mortality schedules, the model provides a tool for understanding the impact of various conditions on the population of the red ape. For example, hunting female orangutans at even a low rate can cause a significant decline in the overall population. Other factors, including catastrophes, habitat quality, and habitat availability can also influence the fate of the species over long periods of time. Significantly, some of the simulated scenarios suggest that if habitat is protected, many of the larger habitat units (populations) will be able to sustain themselves over many, many years.

The other main part of the PHVA involved the discussion between the participants as how to best formulate priorities for scientific study and management of the species as well as communication and cooperation among government and non-government organizations in developing and delivering conservation and education programs.

Clearly, these data and recommended conservation strategies need to be communicated to the wildlife conservation and conservation education community as well as Indonesian and Malaysian wildlife managers and administrators who are ultimately responsible for the management of orangutan habitat. Websites of organizations listing population sizes need to be updated to reflect these new figures. While the next PHVA for the orangutan will probably not take place for another decade, future surveys will now be able to accurately gauge the effectiveness of our collective conservation strategies to insure the protection of the forests and the long-term survival of the orangutan.

The big question is can we stay committed over the next decade to the goal of protecting all the populations of wild orangutans by confronting those forces that would have you believe all is well in the forests of Borneo and Sumatra?

Update to this FAQ page: During recent workshop of orangutan specialists (Brookfield Zoo, Chicago, October 2007), Sumatran orangutan experts downgraded the number of Sumatran orangutans to 6,700. Others at the workshop indicated that the Bornean orangutan had an overall population of 54,700.