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Two Decades of Proboscis Monkeys: A Conservation Success Story in Sabah
Kyoto University, Japan (2024–2025) | Master's Thesis Research
The flooded forests along Borneo's Kinabatangan River in Sabah, Malaysia are home to one of the largest remaining populations of proboscis monkeys -a species found nowhere else on Earth. But how are they really doing? For my master's research, I set out to answer this question by looking back at more than 20 years of population data, creating one of the longest-term studies ever conducted on this charismatic species in the location.
What We Did
This project was not the typical "walk in the forest" fieldwork. Over several weeks, I conducted boat-based surveys along over 223 kilometers of the Kinabatangan River scanning the riverbanks for proboscis monkeys in 2025. With the 2025 population data, I compared it with previous surveys that were conducted in 2014 and 2005. I also combined my new observations with long-term data stretching back to 2005, creating a two-decade timeline of population changes alongside populations at three key monitoring sites. Using sophisticated statistical models -state-space model & GIS- I analyzed not just the population dynamics of the proboscis monkey, but also assessing how land use and forest cover had changed within their potential habitat from 2005 to 2025.
What We Discovered
The results were encouraging:
Good news for proboscis monkeys:
Overall population estimates in 2025 were higher than they were in 2005, suggesting the species is holding its own or even recovering in this region.
Stability matters:
Across the long-term monitoring sites, population sizes remained stable -no dramatic crashes, which is exactly what wildlife conservationists -including myself!- hope to see.
Forest is returning:
When I analyzed satellite imagery, I found that natural vegetation had actually increased over the study period. Importantly, there was little conversion of forests to oil palm plantations, particularly within the protected areas (Wildlife Sanctuary and forest reserves), thanks to the Sabah state government on their efforts in protecting forests and minimizing deforestation.
Why It Matters
This research offers something rare in conservation: genuine hope. While proboscis monkeys remain endangered, our findings suggest that protection efforts in the Lower Kinabatangan are working. The stability and modest growth we documented here likely reflect decades of integrated conservation work -establishing protected areas, restoring degraded forest, and maintaining wildlife corridors.
But there's a concern apart from our results. Other populations of proboscis monkeys from different locations in Sabah did not show the same positive trends. The fact that deforestation is ceaseless in other unprotected forests pose a threat to their survivability. Protecting every remaining patch of forest, and continuing to restore degraded areas, remains essential for their long-term survival in Sabah, and Borneo Island as a whole.
Nonetheless, for me, this project was a powerful reminder that conservation is a marathon, not a sprint. Two decades of monitoring -by multiple researchers across generations- allowed us to see the big picture. And that picture, while not perfect, is genuinely encouraging. Continuous surveys and monitoring in the future is crucial to better understand their population dynamics in the midst of ongoing anthropogenic development.
Disclaimer: This research represents my Master's thesis work and is being prepared for peer-reviewed publication. The findings described here are based on analyses completed in 2025.
Parasites and Proboscis Monkeys: Effects of Group Size and Gradients of Habitat Disturbance
Kyoto University, Japan (2024–2025) | Collaborative Research Project
Deep in the riverine forests of Sabah, Malaysian Borneo, lives one of the most unusual primates on Earth: the proboscis monkey. With their impressive noses, potbellies, and striking reddish-brown fur, these endangered monkeys face increasing pressure from habitat loss. As a flagship and charismatic species, they are important not only as a forest health indicator but also crucial for sustaining the livelihood of the local residents through ecotourism. In this study, I investigated a microscopic yet essential aspect of their health -the parasites living inside their potbellies!
What We Did
Along the Menanggul River, a tributary of Sabah's Kinabatangan River, fecal samples from free-ranging proboscis monkey groups were collected. Back in the lab, we (led by Prof. Ikki) teamed up with parasite expert Dr. Liesbeth Frias to examine these samples under microscopes and identify any parasite eggs or larvae present. We then used Bayesian statistical models to explore whether factors like group type, group size and habitat disturbance influenced infection rates by the parasites of the monkeys.
What We Discovered
The results were striking:
Widespread infection:
A remarkable 81.25% of the monkeys sampled showed evidence of parasite infection -meaning the vast majority carried at least one type of intestinal parasite, consistent with other findings in different locations and settings.
Three main culprits:
We identified three dominant parasite groups, Trichuris sp., Strongyloides fuelleborni, and Oesophagostomum aculeatum and such parasites can also be found most wild primate populations -even humans!
Patterns in infection:
The number of parasites an individual carried wasn't random but conditional -although no significant patterns were observed between parasite abundance and group type, it varied significantly with both how large their social group was and the condition of their surrounding habitat. These variations was taxon-specific: Trichuris sp. was positively correlated with group size while S. fuelleborni and O. aculeatum correlated negatively. On the other hand, Trichuris sp. was able to thrive under strong anthropogenic disturbances, but conversely with O. aculeatum.
Why It Matters
Parasites are a normal part of ecosystem health, but changing conditions can upset the delicate balance between host and parasite. Proboscis monkeys are already endangered, and understanding how social factors and habitat disturbance affect their health gives conservation managers valuable insights. If larger groups or degraded habitats lead to higher parasite loads, these factors may need to be considered when planning protected areas or habitat restoration efforts.
This project was a fascinating glimpse into the hidden world of wildlife health -and a reminder that conservation isn't just about protecting habitat, but understanding the complex interactions that determine the animals' survivability, especially in this ever-changing environment where the paths of wildlife, livestock and humans are easily intersected.
📄 Read the peer-reviewed paper: https://doi.org/10.1016/j.ijppaw.2026.101221
Activity Patterns of of Dusky Langurs in Penang Island, Malaysia: Does Age Makes a Difference?
Universiti Sains Malaysia (2019–2020) | Bachelor's Thesis Research
For my Final Year Project of Bachelor's degree, I spent almost a year observing a fascinating group of dusky langurs -colobine, leaf-eating monkeys with dark silver fur and expressive spectacled-like patterns around their eyes and bright yellow babies- living along the coast of Teluk Bahang in Penang. What made this group special was their unique home: a patchwork landscape combining natural forest, a modified eco-tourism park, and beachfront areas.
What We Did
Every week, I followed the same group of langurs, carefully recording their behaviors and tracking their movements using GPS. My goal was to understand how these primates spend their time and whether younger monkeys behave differently from adults. Over the course of the study, I collected nearly 3,300 behavioral observations: 1,716 from adults and 1,521 from juveniles.
What We Discovered
The data revealed some clear patterns:
Age matters:
Juveniles spent significantly more time moving and playing than adults -not surprising, given that young animals everywhere use play to develop strength and social skills.
Family matters:
Adults were more involved in carrying and caring for infants, a responsibility that juveniles haven't yet taken on.
Everything else:
When it came to feeding, resting, and social grooming, adults and juveniles behaved quite similarly. I also found out that they not only forage inside the forest, but also prefer to spent some time foraging on the trees near the beach. Due to the presence of asphalt road separating the forests and the coastal areas, they had to cross the busy road, endangering their life.
Why It Matters
Understanding how wild primates use human-modified landscapes is increasingly important as development expands into natural habitats. This research shows that dusky langurs can adapt to areas with regular human activity, but also highlights which habitats they consider essential - information that can guide conservation efforts in Penang and beyond.
When this study was conducted, there was a canopy bridge installed by the Langur Project Penang, with the hopes of facilitating arboreal animals -like the dusky langurs- to safely cross the road and minimizing the number of road-kills. Although I observed some individuals utilized the bridge, however, since the installation was fairly recent, other individuals from the group haven't fully habituated with the presence of a new foreign object. I believe in time, the langurs will confidently utilize the bridge once they are comfortable, without having to put their lives at stake!
Disclaimer: This research represents my Bachelor's thesis work with collaboration and field supervision by Langur Project Penang. All rights reserved.
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