Hsin Chien Tsai, Po-Jen Chiang, Jamie Bolam, Chium Tse Huang, Ching Hua Yang, Ho Tsung Chu, Ming Chuan Li, Kun Sung Wu

The Formosan black bear (Ursus thibetanus formosanus) is an endangered subspecies endemic to Taiwan. While historically restricted to remote mountain ranges, recent observations suggest a population expansion into Zhuoxi Township in Eastern Taiwan, leading to increased human-bear conflicts. This study provides Taiwan’s first rigorous black bear density estimates by integrating Indigenous participatory monitoring with Spatial Mark-Resight and Spatially Explicit Capture-Recapture models to guide conflict mitigation. We employed a three-tiered approach: (1) Semi-structured interviews (n=38) to document local Traditional Ecological Knowledge (TEK) from Indigenous communities regarding bear trends; (2) Systematic camera trapping (2021–2025), which evolved into 2*2 km monitoring grid in late 2024 to track distribution; and (3) Density estimation using a 4*4 km grid (n=17 stations) in 2025. We utilized high-hanging honey baits to elicit standing behavior, enabling individual identification via unique chest markings from camera trap images. Results from TEK and biological monitoring were highly consistent. 84% of residents perceived an increase in bear abundance over the last decade. The camera trap Relative Abundance Index (RAI) doubled from 0.38 to 0.77 events per 100 trap days (2021–2024). In the 2025 survey, 13 unique individuals were identified and utilized for density modeling. SECR estimated a density of 14.1±7.3 bears/100 km² , while SMR models further supported these findings with estimates ranging from 11.6 to 24.6 bears/100 km². These results are significantly higher than historical estimates. These findings confirm that while the species remains endangered, local populations in Eastern Taiwan are recovering and expanding into the human-wildlife interface. Conservation must shift from passive protection to proactive coexistence, integrating Indigenous partnerships and conflict mitigation to ensure the sustainable recovery of this iconic species.