Distribution and Habitat Characteristics of the Müller’s Gibbon (Hylobates muelleri) in a Degraded Sub-watershed Landscape of South Kalimantan, Indonesia

The Klampiaw gibbon (Hylobates muelleri), an endemic primate of Borneo, faces increasing threats from habitat fragmentation and deforestation. This study investigates the spatial distribution and habitat characteristics of H. muelleri in the Kusan Hulu sub-watershed, South Kalimantan, Indonesia. Field surveys conducted between July and September 2024 employed line transects, vegetation sampling, and habitat assessments across land cover types including secondary forests, agroforestry areas, and degraded lands. Results indicate that H. muelleri is mainly found in secondary forests with dense canopy cover, tall tree structures (>20 m), and the presence of key food sources such as Ficus and Artocarpus species. Gibbon groups tend to avoid open and plantation areas with low tree diversity and limited vertical complexity. Sixteen individuals were recorded across four observation zones, with the highest encounter rate (1.5 individuals/km) in well-connected forest corridors. Importance Value Index (IVI) analysis revealed dominant tree species that support gibbon foraging and movement. Conservation actions should focus on protecting natural habitats, restoring degraded areas with food tree species, reducing anthropogenic disturbances, and involving local communities in habitat management. These findings support evidence-based conservation planning for H. muelleri in tropical watershed landscapes and provide insights into the ecological requirements of Bornean gibbons. Keywords: Hylobates muelleri, habitat preference, secondary forest, IVI, tropical watershed, conservation strategy