Spatial patterns and ecological determinants of Himalayan brown bear distribution in the Trans-Himalayas of India

The Trans-Himalayan region of Ladakh is home to the endangered Himalayan brown bear, a species that remains understudied in high-altitude environments. In the Indian Himalayas, brown bears are threatened by low population densities, and isolated, insular populations. Brown bear presence points in this landscape were collected through trail transects using polygon search framework in a systematic, grid-based manner covering ~ 35,100 km² (275 grids) with 4012 trails ranging from 0.5 to 6.78 km. A total of 2530 brown bear signs were recorded across the logistically possible surveyed region of the total 680 grids (10 X 10 km²). We employed occupancy framework to understand the environmental and anthropogenic factors influencing brown bear distribution while accounting for imperfect detection. The best occupancy model (selected from 36 candidate models based on AIC) indicated a significant positive influence of terrain ruggedness, rangelands and water availability, and land surface temperature to brown bear occupancy in the study region. Further, we used MaxEnt to model potential brown bear habitats in the Trans-Himalayan landscape. The best-performing model (out of 35 models, evaluated using AUC and TSS) showed that temperature seasonality, elevation, human footprint, and land use/land cover best explained the suitable brown bear habitats in the study area. Our study provides first comprehensive landscape-scale baseline assessment on the distribution of Himalayan brown bear in high-altitude region, and highlights the key environmental driver, particularly terrain and temperature variation, influencing its occupancy and distribution. These findings are expected to inform policymakers and conservation practitioners in formulating targeted strategies to mitigate the potential impacts of climate change on this endangered species.