In the northeastern region of China, winter is characterized by a snow-covered period that can last up to half a year, with frigid temperatures and scarce food resources. To cope with these harsh environments, Asiatic black bears (Ursus thibetanus) hibernate during most of the winter, a period that also coincides with their breeding and early cub-rearing phase. Therefore, hibernation is crucial for the stability of populations in this region, and suitable dens are essential for successful hibernation. This study, conducted between 2015 and 2019 in the Wangqing National Nature Reserve in Jilin Province, identified 24 dens sites through field surveys. Using descriptive statistics, principal component analysis (PCA), and random forest modeling, we examined den structure, microhabitat, and denning habitat to explore the factors influencing den selection and the environmental factors affecting den site choice, thereby revealing the relationship between the microhabitat, denning environment, and den selection. We found that the trees selected for denning were primarily Populus cathayana, indicating a relatively narrow range of tree species compared to other studies. The denning trees had a diameter at breast height (DBH) of approximately (122. 89 ± 13. 60) cm, with den entrances measuring about (39. 26 ± 6. 62) cm in diameter. The orientation of the den entrances fell within the range of solar altitude and was sheltered from the wind, suggesting that temperature plays a significant role in den entrance selection. Entrance orientation accounted for most of the first principal component, and the DBH and entrance size constituted the second principal component. Together, these two components accounted for 0. 85 of the total variance, indicating that entrance orientation, DBH, and entrance size are the primary factors considered in den selection. The main factors influencing den site habitat selection included the distance to rivers, distance to major roads, gross primary productivity (GPP) in October, and distance to human settlements. The ecological significance of these factors suggests that the primary considerations in den site selection are safety, insulation, and access to food resources. This study provides scientific support for the conservation and restoration of denning habitats for Asiatic black bears in northeastern China.
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