How vulnerable are denning bears to disturbance?

When exposed to human disturbance, most large carnivores are able to move a way from the source with little energetic cost. Bears represent an exceptio n in that during winter, most individuals spend several months in an energy -saving state of hibernation in a den. This implies that disturbance of den ning bears has the potential to have a large energetic cost, although data on the subject are rather diffuse. We reviewed the literature on densite se lection, denning physiology, and responses to disturbance for the brown bea r (Ursus arctos), black bear (U. americanus), and polar bear (U. maritimus) . Generally, bears select dens one to 2 km from human activity (roads, habi tation, industrial activity) and seemed to tolerate most activities that oc curred more than one km from the den. Activity closer than one km and espec ially within 200 m caused variable responses. Some bears tolerate disturban ce even inside the den, but bears will abandon dens in response to activity within this zone, especially early in the denning period. Den abandonment by brown and black bear females with cubs of the year can lead to increased cub mortality. Specific excavated or ground dens are rarely reused, wherea s natural caves or hollow trees are reused with varying frequency. There is often some distance between an individual bear's consecutive dens. This in dicates that loss of a single denning area following human disturbance will not always lead to deleterious effects, ii alternative denning areas are a vailable within the home range.