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Once thought to be on the verge of extinction in Singapore, the Critically Endangered Raffles’ Banded Langur is predicted to have a population of around 244 individuals by 2071. These findings emerged in a recent paper “Population viability analysis of the population of Raffles’ banded langurs Presbytis femoralis in Singapore”, published in the Raffles Bulletin of Zoology in September 2023. Based on the model calculations, the population is projected to double in the next 15 years from 75 to over 150.
Co-authored by researchers from Singapore and the Oxford Brookes University in the United Kingdom, the latest findings are contrary to previous research conducted in the 1990s where it was suggested that the population of Raffles' Banded Langurs was likely to go extinct within 40 years due to habitat loss and fragmentation.
“The results presented in our paper show that with the right protection and management measures in place, we can bring a species back from the brink of extinction. However, these endeavours demand steadfast dedication in the field, strong partner collaborations and adequate financial support. While the progress we are witnessing is inspiring, there is still much to be accomplished in preserving the Raffles’ Banded Langur and Singapore’s natural heritage, which includes the protection of remaining habitats,” said primatologist Dr Andie Ang, Head of Primate Conservation and Singapore Programmes at Mandai Nature and chairperson of the Raffles’ Banded Langur Working Group.
Singapore is home to one of the rarest and most threatened primate species globally - the Raffles' Banded Langur. Named after Sir Stamford Raffles who noted the species as new to science in 1822, it is highly arboreal, feeds primarily on leaves and other plant parts, and is characterised by its black fur and white bands on the chest and inner legs.
Efforts to conserve the remaining populations of the species have steadily improved its outcomes over the years. In 2016, the Raffles’ Banded Langur Working Group was formed through a partnership of various organisations and agencies in Singapore and Malaysia, to drive and deliver on conservation goals for the species. Local partners include the National Parks Board of Singapore (NParks), which acts as the national scientific authority for biodiversity conservation in Singapore, as well as academics from local universities and nature groups.
Managed and funded by Mandai Nature, the Working Group has been spearheading a Species Action Plan with measures that have led to improved habitat protection, population research and public awareness for the langurs. This involves conducting field research to gather data on the population’s distribution as well as ecology and behaviour. Data collected have been used to facilitate discussions and advance collaborations with NParks, which will work with relevant agencies and the community, including researchers, to enhance the langurs’ habitats and facilitate safe movement through a range of conservation and ecological connectivity measures.
Another key aspect of the Species Action Plan is to engage in public outreach and advocacy initiatives which saw the launch of a citizen science programme aimed at raising the profile of the species in Singapore. Now in its seventh year, the programme has successfully involved over 520 volunteers since its inception.
Despite the positive results arising from the study, the researchers emphasised that even a slight increase in deaths within the population could lead to a reduction in population size within the next 50 years.
The team used ecological software to model growth of the population under different threat and management scenarios. The results identified the loss of unprotected habitat as the greatest current threat to the population, whilst the most effective short-term management strategy was the enhancement of connectivity between forest fragments in their existing habitat.
The langurs are particularly vulnerable to fatalities from road-related accidents, which occur when they attempt to cross busy roads between forested areas. Between 2017 and 2023, four individuals – which constitute around 5 per cent of the total population in Singapore – died from collisions with road vehicles.
“Although our model shows the population is likely to continue growing in the next 50 years, they remain vulnerable to not only deaths from roadkill, but also unpredictable events such as diseases and extreme weather,” cautioned Amy Woolloff, the paper’s lead author. “To ensure the long-term survival of this species in Singapore, there remains an urgent need to identify more suitable habitats for the Raffles’ Banded Langurs, to enhance habitat connectivity to prevent deaths occurring from road crossings, and to increase population genetic diversity with conservation translocation”.
Whilst acknowledging that there is always more work to be done, both NParks and the research team are pleased with the progress achieved in the conservation of the Raffles’ Banded Langurs in Singapore, which serves as a noteworthy example of successful management of a Critically Endangered species, and hope strategies used in Singapore can be replicated in similar populations globally.
Mr Lim Liang Jim, Group Director of Conservation, NParks, said: “To protect the local Raffles’ Banded Langur population, which hit a low of 10 individuals in the 1980s, NParks has implemented a range of habitat enhancement measures. These efforts are guided by our Nature Conservation Masterplan (NCMP), which sets out our strategies to safeguard key habitats in Singapore. A key thrust of the NCMP is community involvement, and NParks has been working with the community to improve the langurs’ habitats through reforestation and enrichment plantings. For example, Thomson Nature Park was sensitively enhanced with the planting of food plant species. Canopy linkages were also enhanced with the planting of tree species that have spreading canopies. NParks also installed rope bridges along Old Upper Thomson Road, which separates the nature park from Central Catchment Nature Reserve, to further facilitate the safe movement of the langurs. In assessing where to situate the rope bridges, NParks worked closely with the Raffles’ Banded Langur Working Group to locate them where the langurs have been observed to habitually cross. NParks will continue to work with the community to come up with strategies to strengthen the survival of our native langurs and other wildlife.”
The full paper can be accessed here.
