Remaining populations are scattered in highly fragmented habitats, including near croplands within urban areas. There is an urgent need to locate viable populations and designate key conservation areas for this critically endangered species. More data on the population trends, ecology, and population genetics are urgently needed. There is also a need to raise awareness about this species in order to generate public and government interest.
The distribution of P. percura requires clarification. It is known to occur in Giam Siak Kecil-Bukit Batu Biosphere Reserve in Sumatra, Indonesia through camera trap surveys (Fujita et al. 2012), but no other information is available.
The species is protected under the name Presbytis melalophos in Indonesia’s 2018 protected species list. No harvest quota has been allocated for any of the Presbytis species for at least since 2000 and no animals are allowed to be taken from the wild for commercial purposes.
Location InformationThis species is endemic to the Riau Province in east-central Sumatra, Indonesia. It is distributed from the Rokan River in the north to at least the Kampar River in the south (Wilson and Wilson 1977, Kawamura 1984, Aimi and Bakar 1992, Rizaldi et al. 2019). The southern limit of P. percura is currently unknown, though preliminary research showed that P. siamensis cana occurred from at least the south of Kampar River to Indragiri River (Roos et al. 2014, Rizaldi et al. 2019). Field studies on the distributions of Presbytis spp. (P. bicolor, P. percura, P. siamensis cana) in Riau Province are urgently needed.
There is no estimate on population size in the wild for this species. However, it is suspected that the species has undergone ≥80% population decline over the last three generations since 1984 (30 years approximately; see Nijman et al. 2020) due to habitat loss and degradation and fragmentation, as well as retaliatory killing.
Little is also known about their ecology, behaviour, and genetics. Known populations were located in isolated forest fragments separated by oil palm and rubber plantations. A total of nine groups and 75 individuals of P. percura were observed during an eight-day preliminary field survey (Rizaldi et al. 2019). The group size ranged from two to 15 individuals. Two dependent infants and a few juveniles were also seen.
Presbytis percura faces a high risk of extinction in the wild. Its natural habitats are rapidly converted to agricultural land. Compared to other provinces in Sumatra, Riau experienced the highest rate of deforestation, where 63% of the natural forest have been lost between 1985 and 2008. Riau also produced more palm oil and paper pulp (Uryu et al. 2010). These land use changes have resulted in highly fragmented forest remnants and degraded habitats that are surrounded by oil palm, rubber, and forest plantations (e.g., Acacia spp. and Eucalyptus spp.) within the range of P. percura. Additionally, forest fires due to hot weather conditions and open burning for agricultural purposes destroy millions of hectares of land in Indonesia on an annual basis, and Riau is often one of the worst impacted areas, owing in part to its high concentration of peatland (World Bank 2016). Individuals of this species were also killed by local communities when they fed on fruit crops such as rambutans, durians and mangosteens.