Tricolour langur (Presbytis chrysomelas cruciger)
Mohamed bin Zayed Species project number 232533165
Conserving Borneo’s Rare Tricolour Langur (Presbytis chrysomelas ssp cruciger): Mapping, Protecting and Safeguarding their Habitat in West Kalimantan, Indonesian Borneo
The Tricolour Langur: One of the World’s Most Endangered Primates
The tricolour langur (Presbytis chrysomelas cruciger), one of two subspecies of the Bornean banded langur, is ranked among the 25 most endangered primates in the world. Both subspecies are classified as Critically Endangered on the IUCN Red List and listed under CITES Appendix II. Once abundant across northern Borneo, these charismatic primates now face an uncertain future, having vanished from 95% of their original range.
Where They Live: From Rainforests to Rubber Plantations
Tricolour langurs are lowland forest specialists, inhabiting tropical wet evergreen, peat swamp, and freshwater swamps forests. However, these adaptable primates have also been observed in agricultural areas, particularly smallholder rubber tree plantations. Despite this evidence of their adaptability, their range has been severely reduced, with a 50% decline since 2000. In fact, the tricolour langur now has the most restricted range of all Presbytis species.
Caught in the Crossfire: Habitat Loss and Hunting Threaten Langurs
Habitat conversion has been the biggest threat to the tricolour langur in recent years. Extensive agricultural development, especially for oil palm, has led to a devastating loss of Borneo’s lowland forests, crucial for the langurs’ survival. With nowhere else to go, this large-scale lowland forest clearance poses an existential threat to the tricolour langur. Langurs are further threatened by hunting throughout their range.
Bentarum, a Tricolour Langur Stronghold
Located in the district of Kapuas Hulu, the Bentarum landscape includes the hilly and mountainous terrain of Betung Kerihun National Park and its 800,000-hectares of forest, in the north. Danau Sentarum, renowned for its unique seasonal lake ecosystem, protects 127,348-hectares of forest in the south. Between the two parks lies the Bentarum corridor, a 315,000-hectare multi-use landscape that encompasses lush forests, meandering rivers, and rich biodiversity.
Sangga Bumi Lestari is implementing a multi-year project in Bentarum, with four main objectives:
1. Improve indigenous management of approximately 100,000-hectares of forest.
2. Increase conservation of Bentarum’s wildlife.
3. Enhance forest connectivity.
4. Empower communities to manage forest areas.
Once thought not to occur in Kalimantan, the tricolour langur was confirmed in Danau Sentarum in 2020. Sangga Bumi has seen the langur outside Danau Sentarum in the Bentarum corridor.
To understand the distribution of the tricolour langur in Bentarum, with the kind support of The MBZ Conservation Fund, Sangga Bumi conducted surveys in 33 transects covering ssix habitat types, over 165km in five villages. Befitting its Critically Endangered status, langur groups were observed on just five occasions. We detected four groups of tricolour langurs from two transects identified as an undisturbed peat swamp ecosystem and one group in habitat identified as a mixed agriculture ecosystem. The results produce a low density rate of 1.481 groups/km2 in peat swamp forests, which is their main habitat. Extrapolation would indicate a total population of 7,391 individuals in Undisturbed Peat Swamp and 154 individuals in Mixed Agriculture Ecosystems. This would be higher than the populations reported in other locations in Malaysia. However, with such a low detection rate, we are cuatious about this population size.
A Risky Safe Haven
Sangga Bumi staff have seen tricolour langurs being eaten and villagers openly admit to hunting them. To understand the wider distribution of tricolour langurs outside of transects and the extent of the hunting threat, Sangga Bumi conducted field observations across Bentarum, social surveys with 198 household representatives in eight villages, and workshops with villagers to better understand hunting dynamics.
Tricolour langurs are observed by villagers throughout Bentarum (with the caveat that there is potential misidentification with the overlapping maroon langur). In every area they live, tricolour langurs are hunted. Hunting is a deeply embedded cultural practice in Bentarum. It is also indiscriminate, with only orangutans covered by cultural taboos.
84% of hunting is for wild meat consumption. Local hunting practices for wild meat, which are part of cultural traditions, have been influenced in recent years by the arrival of African Swine Fever (in 2020) and frequent waves of Newcastle disease. These zoonotic diseases have decimated wild and domestic pig populations and domestic chicken populations respectively. It’s not a linear increase, but there is now a greater reliance on wild meat as a result of reduced domestic livestock.
The dynamics are extremely complex, driven by cultural beliefs, views (often incorrect) on disease risk, a belief that livestock can only be fed by expensive industrial feed, and observed cases of malnourishment-induced stunting in the landscape and the advice of the government to mitigate this by eating more meat.
Increasing Community Resilience through Sangga Health
All these insights have led to the development of our Sangga Health project. Through Sangga Health, we seek to reduce rates of hunting and mitigate threats to biodiversity through increased availability of disease-free livestock, improved public health, and the advancement of culturally appropriate indigenous management systems. The tricolour langur will become a target species for Sangga Health.
Sangga Health the potential to significantly reduce risks to the tricolour langur. We are grateful that the support of Mohamed bin Zayed Species Conservation Fund has allowed us to develop this programme.