Habitat Protection


Batang Toru

Despite the fact that the majority of the remaining Sumatran orangutan population resides north of Lake Toba in the Leuser Ecosystem conservation area, there is a very unique and less known population of Sumatran orangutans living south of Lake Toba in a forest area now commonly referred to as the Batang Toru Forest Complex. This forest complex is divided into two forest blocks (i.e. east and west Batang Toru), which are found in the North Sumatran districts of Central, North, and South Tapanuli. The Batang Toru monitoring station, located in the West Batang Toru Forest Block, is made up of a mix of hill dipterocarp forest, submontane forest, and upland heath forest. This relatively new SOCP monitoring station, established in 2006, is highly unique in that it houses the only viable Sumatran orangutan population south of Lake Toba and is also the only Sumatran orangutan monitoring station that is located in an upland forest setting.

Early surveys (1997, 2000-2001, and 2003) in this area were conducted under the direction of Dr. Erik Meijaard and subsequently by Dr. Serge Wich, with logistical and financial support from the Golden Ark Foundation. However, it wasn’t until 2006, when PanEco’s Dr. Gabriella Fredriksson and Graham Usher, in collaboration with local counterpart NGO Yayasan Ekosistem Lestari and the SOCP, established the Batang Toru monitoring station in the West Batang Toru Forest Block. During the early years of the Batang Toru monitoring station, a trail system and numerous phenological plots were established by YEL staff members Tri Wahyu S. and volunteer station coordinators Dr. Helga Peters and Gregoire Bertagnolio. In addition, the habituation process of the local orangutan population was started, so that long-term behavioral data could be collected.

Between 2008-2010, as a part of larger genetic study being undertaken by Dr. Alexander Nater, Dr. Natasha Arora, and Dr. Michael Krützen from the University of Zurich, DNA samples from the Batang Toru orangutan population were collected. The most recent results from the Evolutionary Genetics Group at the University of Zurich suggests that the Batang Toru orangutan population is genetically unique, and that potentially as a result of a series of ancient eruptions from the famous Toba volcano, the northern and southern Sumatran mitochondrial gene pools are highly divergent, with the Batang Toru population showing greater similarity to Bornean orangutan populations. While these same genetic patterns are not present in the results from the Y-chromosome data, likely due to long-distance male dispersal patterns, the consensus results for the Batang Toru orangutan population indicate that they represent a relic population from a more expansive central and south Sumatran orangutan population, which is now extinct except for the Batang Toru populations. Due to their genetic uniqueness, the Batang Toru orangutan population probably deserves the highest conservation effort.

In 2010, PanEco’s Matthew Nowak, then from Southern Illinois University-Carbondale, began to conduct his PhD research on the Batang Toru apes, including gibbons, siamangs, and orangutans. His project, which lasted until the beginning of 2013, focused on the comparative locomotor behavior and canopy use of these unique primates. Matthew’s project was funded by the United States National Science Foundation. He is currently in the process of analyzing and writing up his results.

Despite the fact that the Batang Toru orangutan population is the only large viable orangutan population that is south of Lake Toba and that it is now known to be genetically distinct from the orangutans that inhabit forested areas north of Lake Toba, only about 25% of the Batang Toru Forest Complex is protected. As such, the orangutans of Batang Toru are still under threat from destructive and extractive human activities, such as logging, mining, and hunting. Nevertheless, PanEco and Yayasan Ekosistem Lestari are in the process of petitioning the Indonesian government and other relevant stakeholders to change the status of the remaining primary forest in Batang Toru to protection forest. These changes, while highly important for maintaining the unique floral and faunal diversity in the Batang Toru Forest Complex, are also of vital importance for maintaining a stable ecosystem, providing water, and other environmental services, which in turn are important for the economy and daily lives of local communities living in and around Batang Toru.

Since its inception in 2006, the Batang Toru monitoring station has assisted 1 PhD research project and 10 bachelor’s projects. Currently, there are eight full-time SOCP-YEL staff members who are monitoring habituated members of the orangutan population and the phenological characteristics of the Batang Toru station. These data, once fully analyzed, will help shed light on the behavioral ecology of this unique and residual upland orangutan population. The Batang Toru monitoring station has primarily been funded by BOS Netherlands, the Durrell Wildlife Conservation Trust, Great Ape Trust, Ouwehands Zoo Foundation, and the PanEco Foundation.


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