Sumatran and Tapanuli orangutans are found only on the Indonesian island of Sumatra. With just over 13,000 individual Sumatran orangutans (Pongo abelii) and approximately 800 Tapanuli orangutans (Pongo tapanuliensis) left in the wild, both species are at severe risk of extinction.
Long-term monitoring and studies of species and their habitat are integral to understanding orangutan behavioral ecology and conservation needs/threats, especially for such a long-lived and slow reproducing species. The SOCP carries out important surveys and monitoring of both species of orangutan in Sumatra, and we maintain long-term studies of their behavior and ecology across various stations throughout the island. Namely the Batang Toru Monitoring Station and Sikundur Monitoring Station forests of North Sumatra, and at the well-known peat swamp research station at Suaq Balimbing of Aceh; we also conduct extended post-release monitoring of the growing, reintroduced Sumatran orangutan population at the Jantho Nature Reserve, in northern Aceh.
Each site has something interesting to tell, and altogether they serve to paint a more complete picture of orangutan ecology. The Batang Toru orangutans are especially interesting considering recent studies, with in November 2017 there having been declared as an entirely new species of orangutan. Whereas at Sikundur our site is in studying orangutans on the eastern edge of Leuser, and in a post-logging setting, meaning we can find some behavioral differences within and between populations. Suaq Balimbing then is famous as the first ever research site to find orangutans regularly and routinely making and using tools in the wild, due to the extremely high densities and unusually sociable orangutans found there.
At each site the SOCP monitors the orangutan population and collects behavioral, climatological and phenological data.
For purposes of behavioral data collection, habituated orangutans are followed from their nest in the morning to their nest at night. During each follow, trained staff utilize instantaneous focal animal sampling with a 2-minute sampling interval to record orangutan behavior. At each 2-minute sample, observers record the focal animal’s behavioral state, including feed, rest, travel, social, nest, and other (eg autogroom, autoplay, voiding). If an animal is feeding at the time of observation, observers also record the food type and fruit source of the food items being consumed.
Long-term phenological plots are monitored each month. Data collected for each of the long-term plots includes the availability scores of young leaves, flowers, and fruits, which follows the ‘Phenology Sampling Protocol’ developed and standardized by members of the Orangutan Network. Rainfall also is recorded, with the absolute minimum and maximum temperatures noted. Additionally, temperature and humidity are logged each hour with a weather station.
Additionally, the station team will collect detailed species inventories (eg birds, amphibians/reptiles, mammals, plant/tree species) and presence records for all local fauna. Other activities will include trail maintenance, habitat patrols within the station, assisting local/international research projects.
Suaq Balimbing Station
Suaq Balimbing, an SOCP biodiversity monitoring station located in the Kluet swamps, built in 1992, is the only site in Sumatra where biologists are monitoring orangutans in a peat swamp forest setting. In fact, the earliest inhabitants of the Suaq field station were forced to develop a rudimentary wooden boardwalk, just one plank wide, which was built across the main part of the study area, so that they could more efficiently traverse the often-submerged forest floor. This boardwalk system, though it must be continually replaced, is still a major necessity at Suaq to this day.
Suaq has long been the site of a major ongoing research program studying the orangutans and these unique peat swamp forests, with many new discoveries regarding the social structure and ranging behavior of orangutans having resulted from this work. Suaq remains the only forest in Indonesia where orangutans have regularly and routinely been observed making and using primitive tools, which they do on an almost daily basis. One of the research projects from Suaq Balimbing Station identified the first known cases of orangutans regularly making and using tools in the wild and identified the Kluet peat swamps as harboring exceptionally high orangutan densities, in fact the highest yet recorded in the world, reaching 8 per square kilometer.
Sikundur Station
The Sikundur Monitoring Station, located in the Langkat District of North Sumatra in the Leuser Ecosystem, is the latest of SOCP’s biodiversity monitoring stations. It consists of primarily lowland dipterocarp and alluvial tropical rainforest habitat. The Sikundur station is the first orangutan research site on the eastern edge of the Leuser Ecosystem, a region that has been largely ignored by researchers due to low orangutan densities, low habitat productivity, and the presence of significant human development. In 2013, the SOCP renovated an abandoned post within the area and developed a 48km network of trails along with 20 phenological plots.
The orangutan population here offers a unique opportunity to evaluate how this Critically Endangered animal is capable of coping with habitat loss and degradation, the study of which promises to help guide future conservation endeavors. The area has had a relatively convoluted and dark past, as it was the site of both small-scale and large-scale logging operations between the years 1976-1988, and then again intermittingly in the 1990s.
Early surveys estimated that the density of orangutans around the monitoring station to be ~1.79 individuals/km2, and SOCP has already habituated 20 orangutans, which are regularly followed by the monitoring team. Until this program, no long-term behavioral or demographic data has ever been collected from any Sumatran orangutan population in an area that has been allowed to recover in this way.
Batang Toru Station
The Batang Toru Monitoring Station – Camp Mayang, located in the west Batang Toru forest block, is surrounded by a mix of hill dipterocarp, submontane, and upland heath forest. This station, established in 2006, is unique in that it is the only orangutan monitoring station in an upland forest setting and the only station focused on studying the Tapanuli orangutan (Pongo tapanuliensis).
Currently, there are 7 full-time team members who are monitoring habituated members of the orangutan population and the phenological characteristics of the forest. Local and international researchers have also helped study the reptiles, amphibians, and even fig and orchid diversity of the site, with a series of field guidebooks now being prepared to document the ecosystem’s richness for others to learn from and enjoy.
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