From the Forest

From the Forest: Orangutan Research and Conservation in Sabangau – The Work of OuTrop


Mark E. Harrison

I became interested in primates at an early age, when I would watch endless natural history documentaries, climbed every tree in sight and even dreamed that, with appropriate surgery, I might be able to live a life in the trees like our primate cousins. Of course, I realize now that this last ambition may have been a little unrealistic, so have instead diverted my attention toward studying and helping to conserve these wonderful animals.

My optimism about working with primates dwindled during the final years of my undergraduate degree, however, as I discovered how difficult it was to get started in this field of work. This changed during a trip to Tanzania. I was travelling alone and went to visit Gombe National Park, which is world famous for the work of Jane Goodall, who was my greatest inspiration during my youth, and its chimpanzees.

Full of excitement, I set foot on the beach at Gombe and went to the national park office to pay my entrance fees, only to find that all of my money and travellers cheques had been stolen on the boat trip over! After making it this far, and meeting other visitors who had seen the chimpanzees, I was absolutely devastated. I never made it back to Gombe, but I resolved there and then that this would not be the end of my “ape experience,” and that I would do all I could to fulfil my (more realistic) childhood dreams.

Fortunately, not long after this in 2003, Helen Morrogh-Bernard offered me a position as her assistant on an orangutan behavior research project that she was establishing in the Sabangau Forest, Borneo, with the Orangutan Tropical Peatland Project (OuTrop).

OuTrop was established in 1999 on the back of Helen and Simon Husson’s undergraduate dissertation research, which was conducted in 1995 as part of a University of Nottingham and Leicester research expedition. Using newly-developed techniques for estimating orangutan population density, they discovered that Sabangau was home to the world’s largest orangutan population.

Simon and Helen have since been joined by many more researchers, including Laura D’Arcy and Dr Susan Cheyne and Dave Ehlers Smith. OuTrop’s remit has grown substantially as a result. We now conduct research into the area’s gibbons, red langurs and cats, plus a number of taxa included within our Ecological Monitoring Project, ranging from trees, to birds, ants and butterflies. Despite this diversification, our core mission has remained the same: to protect Kalimantan’s rich biodiversity through research, training and conservation, particularly within Sabangau.

The OuTrop Team 2012

The Sabangau Forest

Sabangau is one of the best and, at the same time, one of the worst places that I have ever visited. Its biodiversity is staggering: OuTrop and our collaborators have recorded 68 mammal, 167 bird and 218 tree species in the area. At 6,000 km2, Sabangau is also massive, and OuTrop’s surveys have revealed that it is home to the world’s largest population of orangutans (currently estimated at 6,900 individuals) and southern Bornean gibbons. It also contains important populations of many other threatened species. This makes it a very interesting forest in which to do research, and a very important one to understand and protect.

On the down side, Sabangau is also a bit of a nightmare – it is very wet and muddy, which makes getting around the forest incredibly hard work. It is full of insects that bite you, pandan and rattan that scratch you, and roots and logs that trip, tangle and generally just frustrate you. Those expecting spectacular mist-covered rolling hills of forest, dramatic waterfalls and animals leaping from every branch had also better prepare for disappointment – Sabangau is flat, very uniform and animals are very difficult to see. But the animals are there. Yet, so little is known about them and the forest is so unarguably important for conservation, that research here is essential.

Map of Borneo, showing the location of the Sabangau and Kalampangan Forests where OuTrop works

OuTrop performs most of its work in the Natural Laboratory of Peat-swamp Forest, a 500 km2 area in the northeast of the Sabangau Forest. This area is managed by the Centre for the International Cooperation in Sustainable Management of Tropical Peatlands (CIMTROP) at the University of Palangka Raya, who have supported and advised OuTrop’s research since our inception.

CIMTROP also manage the Kalampangan Research Station, which is situated in the Ex-Mega Rice Project Area, on the other side of the Sabangau River. This forest would have been ecologically very similar to that in the Natural Laboratory, but is now heavily degraded. Kalampangan was included in the Indonesian government’s “Mega Rice project” in the 1990’s, which aimed to convert one million hectares of peatland into rice paddies. As predicted by local and international experts, this failed dramatically and turned the area into a fire-prone wasteland. Thousands of orangutans and countless numbers of other species would have perished as a result. This sad story provides a crucial message for conservation in the region, and highlights the importance of protecting Kalimantan’s remaining peat-swamp forests to ensure this ecological catastrophe is not repeated.

Sabangau canopy

Orangutan Research in Sabangau

Population Density and Trends

As our name suggests, OuTrop’s original focus was to understand and protect orangutans in Kalimantan’s peat-swamp forests. Our research began with orangutan population surveys using line transects to count nests. With the exception of very young animals, orangutans will make a nest in the trees each evening and occasionally during the day, which remain visible for a considerable period of time. Wild orangutans are very hard to find (walking hundreds of kilometres of transect would be needed to detect enough individuals to generate a robust density estimate – not easy in this forest), so this method enables population density estimates to be obtained much more easily and cheaply. Using the computer program Distance and various nest-building parameters, these nest abundance data can be converted into an estimate of orangutan population density.

Orangutan population density estimates are incredibly useful for two main reasons. Firstly, they enable identification of important orangutan populations and, hence, forest areas that should be protected. OuTrop’s data showing that Sabangau was home to the world’s largest contiguous orangutan population was a crucial component of the Indonesian government’s decision to assign national park status to the majority of the Sabangau Forest, and has been critical in drawing conservation attention to the area.

Secondly, repeat data collection enables orangutan population trends to be detected, helping us understand the impact of human activities on orangutans. OuTrop have conducted orangutan population surveys annually in Sabangau for the last 17 years, providing a unique long-term data set on population trends. These data are revealing important insights into population trends in the area, starting with a relatively high population density in 1996 before the start of illegal logging in 1997, and a sudden and severe population crash in 2000-2001. (Since the creation of the CIMTROP Patrol Team and cessation of illegal logging in 2004, population density has stabilized and is slowly increasing.)

We believe this crash was caused by illegal logging, forcing orangutans to seek refuge in the low-pole forest. This habitat sub-type is characterized by small trees and so is of little interest to loggers. It is also relatively poor orangutan habitat, owing to the paucity of large fruiting trees. Continued compression of the population into this low-quality habitat over prolonged periods is thought to have led to individuals dying of starvation. Following this crash, the population stabilized as illegal loggers were kept out of the forest. Forest condition has since improved and the population is slowly growing. This theory is supported by shifts in orangutan density between habitat sub-types (in a similar way to that reported by Dr Andy Marshall), and an increase in average tree size in the area.


To understand the behavior and ecology of this important population, OuTrop established its Orangutan Behaviour Project in 2003. This project is still led by (now Dr) Helen Morrogh-Bernard and marked one of the largest changes in OuTrop’s history – the shift from summer-time expeditions, to establishing a full-time, year-round, on-site research team. The project has never looked back and OuTrop staff, interns and students continue to collect orangutan behavior data on an almost daily basis throughout the year. From this success, other year-round research projects have been built (including OuTrop’s Gibbon and Red Langur Behavior Projects), allowing researchers, students and interns to visit the project throughout the year. This year also marked my entry into the project, as Helen’s first non-Indonesian research assistant.

The first period of orangutan behavior research was hugely exciting, as we discovered new individuals and learned new things about the orangutans nearly every day. It was also a very trying, as the animals were not used to our presence in the forest, and so exhibited abnormal behaviors, such as fleeing, extended resting, hiding and continuous kiss squeaking (an alarm call that sounds like a very loud kiss). This led to a long habituation period, in which we followed the animals at a respectful distance and gradually acquainted them with our presence. Over time, the orangutans learned that we were not a threat and resumed their natural behavior, which was what we were interested in recording.

Many interesting and important findings have arisen from data collected by OuTrop’s researchers and students, including studies by Dr Helen Morrogh-Bernard, Kirsten Manduell (PhD data analysis ongoing), Ben Buckley (PhD fieldwork ongoing) and myself. Notable discoveries include that:
• Orangutans in forests with less temporally-variable fruit supplies, such as Sabangau, adopt a search-and-find foraging strategy, compared to the sit-and-wait strategy employed by orangutans in mass-fruiting habitats.
• Orangutans in Sabangau rub an uncommon forest herb into their fur, in what is hypothesized to be the first documented example of wild orangutan topical medicinal use of forest plants. This same plant is used by local human populations for medication post-stroke, and for muscular pains, sore bones and swellings.
• Relatedness among female orangutans in the area is significantly higher than that among males, supporting the hypothesis that male orangutans disperse, whereas females are philopatric.

My own PhD research, conducted at the University of Cambridge with Dr David Chivers, was focused on orangutan feeding ecology in Sabangau and built on the foundations put in place by Helen.

For two years, I completed full-day follows of orangutans in the field to collect data on foods eaten, feeding rates and urine for analysis of ketone production (an indicator of fat metabolism; see Erin Vogel’s From the Forest for details on methods); collected and processed the foods eaten by orangutans (a very arduous process!); analyzed their nutritional and physical properties; and documented orangutan food availability through monthly forest productivity surveys. This revealed that Sabangau orangutans experience periods of energy deficit apparently even longer than that experienced in mass-fruiting forests, which is probably the result of the relatively poor quality of fruit and its consistently low availability in the nutrient-poor peat-swamp forest of Sabangau. Maintaining a favorable energy balance is important, because an animal can only grow and reproduce successfully when it has adequate ‘spare’ energy available, above that needed for simply staying alive.

Combined with similar findings from other sites in Borneo (Gunung Palung/Dr Cheryl Knott; Tuanan/Dr Erin Vogel), this supports the assertion that orangutans are able to survive periods of low fruit availability by metabolising fat laid down during periods where high-quality fruit is abundant. In Sabangau, however, such periods are relatively rare. The demonstration that orangutans in this population suffer frequent and prolonged periods of negative energy balance not only supports the starvation theory behind the 2000-2001 Sabangau orangutan population crash, but also suggests that this population – the world’s largest – might suffer further severe negative consequences if the habitat is degraded further.

Problems and Solutions for Orangutan Conservation in Sabangau

Sadly, both the Sabangau Forest and its orangutans remain vulnerable to multiple human threats.

Our Sabangau study site was logged under concession from 1966-1996 and subjected to intensive illegal logging from 1997-2003, and this disturbance has clearly had a negative impact on forest quality.

Similar stories could be told for almost all peat-swamp forests in Kalimantan – precious few have completely escaped logging disturbance. Logging reduces habitat quality, removes large trees that orangutans favor for food and disrupts their behavior, compromising survival. In particular, the upper canopy layer in Sabangau is punctuated by numerous gaps, with the result that orangutans typically travel through the smaller trees of the more continuous lower canopy layers to save energy. Hunting probably also impacted Sabangau’s orangutans, especially during periods of intense logging.

Although logging has clearly had a detrimental direct impact, it is the indirect effects of illegal logging that pose the greatest threat to the forest and its orangutans. While the concession loggers used rail tracks to remove wood from the forest, the smaller and less well-funded groups of illegal loggers resorted to digging canals into the flooded peat. During the wet season, loggers use these canals to float logs out to the river. These canals are a huge problem, because the formation and maintenance of the peat – upon which the entire forest stands – is dependent on wet, flooded conditions. Under these conditions, dead organic matter cannot rot, leading to a build up of carbon-rich peat and making tropical peat-swamp forests one of the planet’s most efficient terrestrial carbon stores. Once drained and dried, however, peat begins to degrade and becomes highly vulnerable to fire. This threatens the integrity and persistence of the entire forest and releases massive amounts of carbon into the atmosphere, contributing toward global climate change. Peat-swamp forest fires are also incredibly difficult to extinguish, as the peat itself burns below the surface and down to the water table. The negative impacts of illegal logging therefore continue to be felt long after the illegal loggers have left the area.

These threats are being countered through a Community Patrol Team and Fire Attack Force, which is managed by CIMTROP, with support, advice and financial assistance from OuTrop. This dedicated team is comprised entirely of local villagers, helping to ensure support among the local community. The team conduct frequent forest patrols throughout the year to detect and prevent illegal activities. These patrols led to the cessation of illegal logging in the area in 2004, and enable any fires that do arise to be detected and extinguished as rapidly as possible. The Fire Attack Force work under dangerous conditions to fight forest fires, often working around the clock for many days to ensure that fires are properly extinguished. In addition to this, the Patrol Team also work to dam the illegal logging canals that still criss-cross the forest, in order to retain water, restore natural hydrological conditions and prevent fire. To complement these efforts, OuTrop and CIMTROP are developing reforestation programs, to help kick-start forest regeneration in cleared and burnt forest areas.

Fire Fighting

Finally, OuTrop and CIMTROP’s scientists are using their research to help inform and improve conservation policy, and train the next generation of conservationists. This includes advising local government, collaborating with and advising conservation projects in other areas, publishing and disseminating research results, contributing towards species conservation assessments and action plans, and training students, local scientists and villagers.

What Future?

There are many reasons to be pessimistic about orangutan conservation – forest continues to be converted and degraded; recent research by Erik Meijaard and colleagues shows that orangutan hunting is wide-spread throughout Kalimantan; peatlands continue to dry out, burn and degrade, and each new orangutan conservation assessment comes with more dire warnings about the long-term future of wild orangutans.

Yet I believe there is still hope. Yes, orangutan populations are decreasing and becoming increasingly fragmented in many areas, and this pattern is unfortunately likely to continue. The key issue, though, is to protect and secure the survival of those remaining orangutan populations that are still large enough to remain viable in the long term.

And protection efforts can work, as indicated by the gradual increase in orangutan population density in Sabangau due to OuTrop and CIMTROP’s work. Of course, conservation battles are not won overnight and funding conservation projects is always a serious issue, but with the sustained efforts of the many committed conservationists working throughout Indonesia, and support of projects like the Orangutan Conservancy and the general public, I am optimistic that we can prevent the loss of these key populations so that our children might still have the privilege of seeing orangutans in the wild.

OuTrop and I express our deepest gratitude towards all the researchers, staff, students, interns, volunteers and others that have assisted us over the years, CIMTROP for their long-term support and RISTEK for permissions. We are grateful to everyone who has funded us over the years, including the US Fish and Wildlife Great Apes Conservation Fund, Arcus Foundation, Rufford Foundation, Wallace Foundation and Orangutan Appeal UK. The advice of our scientific colleagues, in particular Suwido Limin, Susan Page, Jack Rieley, Erin Vogel, Laura Graham, Cheryl Knott, Carel van Schaik, Maria van Noordwijk, Serge Wich and Matt Struebig is gratefully acknowledged.


Dr Mark Harrison is Managing Director of OuTrop and has been working for the project in a variety of roles since 2003 (Research Assistant, Project Manager, Biodiversity Research Manager and Project Development Leader). He obtained his PhD in orangutan feeding ecology in Sabangau from the University of Cambridge, UK, in 2009; and is an Honorary Visiting Fellow in the Department of Geography, University of Leicester.

Photo Credits 

1. MARK IN KALAMPANGAN, Photo © Eric Perlett/OuTrop   2.  OUTROP TEAM. Photo © Camille Hill/OuTrop  3. SABANGAU CANOPY, Photo © Sonya Gadhia/OuTrop                                4.  ORANGUTAN. Photo © Andrew Walmsley/OuTrop  5. DATA COLLECTION. Photo © Andrew Walmsley/OuTrop 6. FIRE FIGHTING. Photo © Bernat Ripoll/OuTrop

Visit the OuTrop website.

Orangutan Conservancy edit by Tom Mills

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One Response

  1. Thank you very much for having educated us on the work of OuTrop. Thank you for all your efforts in saving our beloved orangutans. Most of us are busy with everyday life that we don’t stop to think about the facts in the paragraph below. Please share these facts far and wide to help making them part of human’s culture. Thank you.


    Your work is important. Please keep doing a great job! Donations will continue to come from our end.

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