Micro-scale selection of winter dens by brown bear (Ursus arctos) males in Southeastern Norway

Den selection is a component of habitat selection, which occurs on several spatial scales. Brown bears (Ursus arctos) in the northern latitudes hibernate in dens during winter, which is their way to survive the period of cold conditions when food is scarce. On the smallest scale habitat selection is the most subtle, and for brown bears it has been found to be more linked to finding security than food. Microscale den site properties can also be important for the thermal conditions in the winter den. A successful denning period is important for the survival and reproduction of bears, which makes it essential to gain knowledge about the possible denning sites for the management of brown bear populations. In this study I examined whether male brown bears in Hedmark Southeastern Norway select for security, food and/or better thermal insulation when choosing a den site on the microhabitat scale. I also studied which factors in the denning habitat may affect the den type and occurrence of ant mounds (Formica spp., Hymenoptera), in which many brown bears use for denning. I used 41 winter dens used by male brown bears between 2001 and 2014 and 160 control points which were placed in the near surroundings of the winter dens. I did all my habitat measurements in the field without using GIS-based habitat data. I found evidence that the male bears in Hedmark selected for security in terms of horizontal consealment, either in the form of an ant mound or surrounding forest. The bears seemed to select for more horizontal concealment when choosing an open den. On the other hand, the bears seemed to select for less vertical cover when choosing an open den, which is probably due to the benefit gained from the thermal insulation from the snow cover. The presence of ant mounds was positively associated with selected den sites and within the denning habitat, ant mounds were more likely to be found in areas with bilberry dominance and in edge habitat