Winter den abandonment by brown bears Ursus arctos: causes and consequences

Winter den abandonment by brown bears Ursus arctos in south‐central Sweden and southeastern Norway was found to occur in 9% of 194 bearwinters, based on 68 radio‐marked bears almost two years old and older. There was no statistical difference between the sexes, between adults and subadults, nor did protection from military or timber‐harvesting activities reduce the rate of abandonment. Although anecdotal, observations suggest that human disturbance was a major cause of den abandonment. Most abandonment occurred early in the denning period, before mid‐winter. Bears moved up to 30 km before denning again. Distance was not related to sex, age, or time of abandonment. Apparently for the first time, a fitness cost of den abandonment is documented: pregnant females that changed dens prior to parturition lost young in or near the den significantly more often than those that did not move.