The orangutan, which is one of the objects of his research, is indicated to inspire stories of short people that have been circulated for generations in the community. Although the story may only be a legend that is difficult to prove, but it is in line with the current reality: these creatures have long disappeared from the forest.

Onrizal, who was born and raised in the area, still remembers vividly the childhood story of a human-like creature that lived in the forest. The legend tells of a creature called the 'short man' by the locals, who disappeared from the forest in the 1970s.

In a recent study popularly published by the environmental news site Mongabay that draws on publications in the prestigious international journal PLOS ONE, Onrizal and other researchers scoured historical records for references to the Tapanuli orangutan (Pongo tapanuliensis). This species is the newest orangutan and is also listed as the most endangered great ape in the world. The Tapanuli orangutan faces a much greater risk of extinction than previously thought.

Today, the Tapanuli orangutan is estimated to occupy only 2.5% of their historical habitat, and the threat of extinction is linked to habitat loss and hunting. This threat persists today and is exacerbated by infrastructure development and forest conversion in the last habitat of the Tapanuli orangutan in North Sumatra. According to the researchers, with habitat shrinking and hunting, the extinction of the Tapanuli orangutan is inevitable.

Currently, as stated in the study, less than 800 individual Tapanuli orangutans live in the Batang Toru forest, North Sumatra. The remaining habitat is estimated to cover only 2.5% of the range in which they lived about 130 years ago when researchers discovered them. That number shrank from nearly 41,000 km2 in the 1890s, to just 1,000 km2 in 2016.

To arrive at these figures, the researchers referred to colonial-era literature, such as newspapers, journals, books and museum records, from the early 1800s to 2019. They found this data in databases, including the Biodiversity Heritage Library and online historical newspapers, books and journals using location-specific keywords such as “Sumatra”, “Batang Toeroe,” and “Tapanoeli,” with Dutch spelling.

The researchers then cross-referenced by searching for terms that specifically refer to orangutans: “orang oetan,” “orang-oetan,” “orangutan,” as well as “mawas,” “mias” and “maias,” which are local names for orangutans that are used commonly in historical literature.

Erik Meijaard, lead author of the study and assistant professor of conservation at the University of Kent, UK, said they had lost a large part of the picture of conservation by ignoring historical information. Historically, the researchers found, the Tapanuli orangutan inhabited a much wider area, and at a lower altitude than the Batang Toru mountain forest they inhabit today.

Much of this historical habitat was lost in the 1950s to smallholder agriculture, before industrial-scale plantation development in Sumatra emerged in the 1970s. The orangutans currently scattered in North Tapanuli, South Tapanuli and Central Tapanuli, are now 52% deforested in the 1930s. The combination of historical fragmentation of forest habitat and unsustainable hunting is likely to push them from the lowland forest areas, where they used to live, to the upland forests of the Batang Toru ecosystem.

Refering to the available information, the researchers think, it is likely that Pongo tapanuliensis was hunted to extinction in an increasingly fragmented part of its former home range. They survive in the remote and rocky Batang Toru Mountains which may have provided protection for orangutans from hunting. These findings show that the Tapanuli orangutan is not a species specifically adapted to live in the highlands as some scientists claim.

Map of Sumatra Island showing the current distribution of Pongo tapanuliensis and Pongo abelii, as well as the main areas mentioned in the study. This finding raises concerns over the survival of the Tapanuli orangutan. Currently, it is estimated that fewer than 800 of these orangutans live in the Batang Toru forest, divided among three connected subpopulations.

The Tapanuli orangutan species face conflicting threats of hunting and killing, as well as habitat loss due to agriculture and plantations. New threats have also emerged, namely infrastructure development, and the construction of hydropower roads which have caused fragmentation of the remaining habitat of the Tapanuli orangutan.

Conservation experts say the most serious threat currently comes from the Batang Toru hydroelectric power plant. The construction of this hydropower plant is considered to endanger the connectivity between orangutan subpopulations in the west, east and south. This fragmentation would cut the diversity of the orangutan gene pool dramatically, leading to inbreeding, disease, and eventually each subpopulation to extinction.

The researchers calculated that more than one percent of adult orangutans disappear from the wild per year, either being killed, translocated, or captured. With that data, extinction is inevitable, regardless of the initial population size.

This analysis shows that the remaining Tapanuli orangutans are in sub-optimal upland habitats and more than 1% of the population is caught every year. This, based on reported kills, translocations and rescues, predicts continued population decline.

According to the researchers' estimation, without further rescue efforts, this species could become extinct in the next few generations. The ongoing fragmentation of the Batang Toru forest only exacerbates this risk. Onrizal called on all stakeholders, including governments, civil society organizations, scientists, donors, local community representatives, and industry, to develop concrete action plans as soon as possible for the survival of this species. (RJ/bs – ©ULC)