Wildlife Biology 20
May 21, 2014
Nathaniel D. Rayl, Todd K. Fuller, John F. Organ, John E. McDonald, Jr., Robert D. Otto and Shane P. Mahoney

The use of day beds for extended periods during the transition into and out of the physiological state of hibernation has been documented in many bear populations, but has never been quantifi ed. Additionally, den abandonment by black bears Ursus americanus has rarely been observed at northern latitudes except after den visits by researchers. In three areas on the northern island of Newfoundland, where male and female black bears spent an average of 158 and 178 d denning, respectively, we identified den sites and extended-use day beds (occupied continuously for 6–26 d) remotely using GPS collars, and here provide the first systematic description of the use of these day beds by bears. We documented den abandonment in 6 (9%; 3 F, 3 M) of 67 bear-winters (6 [14%] of 44 radio-collared bears) and the use of extended-use transitional day beds in 16 (24%) of 67 bear-winters (15 [34%] of 44 radio-collared bears, 8 F, 7 M). In 5 of 10 instances bears left their fall day beds on days with > 15 mm of rain (mean = 28.2 mm, range = 15.6–63.6 mm), which was more than would be expected by chance (p < 0.01). We had more than one year of denning data for 17 bears, 6 (35%) of which reused den sites in diff erent years. Further, we observed some bears using day bed and den sites interchangeably. Though we hypothesized that environmental (flooding) or anthropogenic disturbance (researcher-, forestry-related, or recreational) may have played a role in den abandonment, we found no such relationships, nor was there a difference in the rate of abandonment or day bed use between male and female bears. We could not assess the eff ects of microhabitat attributes, condition, or reproductive status, but acknowledge that these factors may have played a role in den changes.