Primate Research Supplement

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Long-term population monitoring is critical for the conservation of threatened primate species, particularly in biodiverse yet highly vulnerable ecosystems such as the Lower Kinabatangan, Sabah. This region is home to sympatric primates, including the endangered proboscis monkey (Nasalis larvatus), long-tailed macaque (Macaca fascicularis), and pig-tailed macaque (M. nemestrina), all of which are facing increasing threats due to habitat degradation driven by logging and agricultural expansion, especially oil palm plantations. These anthropogenic pressures have exacerbated forest fragmentation, particularly within the Lower Kinabatangan Wildlife Sanctuary—a critical habitat now experiencing significant loss of ecological connectivity. To assess these threats, we analyzed two decades of primate population dynamics across key forest types, using boat-based surveys in the riverine and mangrove forests. Preliminary results indicate that proboscis monkey populations remained stable in both riverine and mangrove forests, while long-tailed macaques showed stability in riverine forests and an increase in mangrove forests. Pig-tailed macaques, which are absent from mangroves, maintained stable populations in riverine forests. Based on these data, we developed predictive models to project population trajectories under various habitat scenarios. While these trends suggest some degree of population resilience, they do not imply an absence of threats. Although boat surveys are effective for counting riparian-dependent proboscis monkeys, they may underestimate ecological pressures on the macaques. The frequent visibility of the macaques along rivers may indicate habitat compression, with their wider forest ranges likely shrinking due to deforestation, thereby forcing them into narrower riverine corridors. To further test this hypothesis, we are employing GIS-based habitat assessments to compare current vegetation with historical data, quantifying the extent of forest loss and its impact on primate distribution. By integrating these findings into state-level conservation planning, this study provides critical evidence to guide the Malaysian government’s strategies for primate habitat protection, corridor restoration, and the development of sustainable land-use policies in the Kinabatangan region.

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