Swenson, J. E., Sandegren, F., Brunberg, S. & Wabakken, P. 1997: Winter den abandonment by brown bears Ursus arctos: causes and consequences. - Wildl. Biol. 3: 35-38.
Winter den abandonment by brown bears Ursus arctos in south-central Sweden and southeastern Norway was found to occur in 9% of 194 bear-winters, 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.
Key words: brown bear, Ursus arctos, den abandonment, disturbance
Jon E. Swenson, Norwegian Institute for Nature Research, Tungasletta 2, N-7005 Trondheim, Norway
Finn Sandegren, Research Division, Swedish Hunters' Association, Box 7002, S-750 07 Uppsala, Sweden
Sven Brunberg, Noppikoski 158, S-794 98 Orsa, Sweden
Petter Wabakken, Environmental Protection Division, Country Governor's Office, Fylkeshuset, N-2300 Hamar, Norway
Received 5 September 1996, accepted 19 January 1997
Associate Editor: Heikki Henttonen