Brown bear hibernation attracts considerable interest not only among scientists but also the general public. Bear dens are often perceived as almost mythical, and common beliefs about their selection and structure do not always reflect reality. This discrepancy results mainly from the difficulty of locating and studying these sites, as well as from methodological biases associated with different survey approaches. At the same time, bear dens require special protection, as hibernating bears can be easily disturbed, which may be dangerous for both humans and animals, especially newborn cubs.
Between 2001 and 2025, a total of 86 brown bear dens were documented in the Tatra Mountains using a combination of telemetry, snow tracking, and incidental observations. Of these, 55 dens were located using telemetry, a method that provides objective and spatially unbiased data on den site selection. Among telemetry-located dens, 14 were situated in caves, 12 were ground nest dens, 10 were excavated dens, and 7 were semi-excavated dens. The remaining 31 dens were discovered through snow tracking and incidental findings: 17 in caves, 7 ground nest dens, 4 excavated dens, and 3 semi-excavated dens. Overall, seven caves and two excavated dens were reused multiple times. Environmental preferences of den sites were analysed, including topography, elevation, and habitat characteristics, to identify factors influencing den selection by bears.
Although both telemetry and tracking can be considered objective methods, tracking is strongly dependent on the presence and persistence of snow cover and therefore is only rarely successful under current climatic conditions. In contrast, incidental discoveries are inherently non-random and biased toward dens that are more visible and accessible to humans, such as caves and excavated dens. This likely leads to an overestimation of the proportion of dens located in such structures when not relying on objective methods such as telemetry.