Den entry behavior in Scandinavian brown bears: Implications for preventing human injuries

Abstract

Encounters between Scandinavian brown bears (Ursus arctos) and humans that result in human injuries and fatalities typically coincide with den entry in October and November, and commonly occur near a den. Our aim was to determine when bears arrive at their dens, identify potential predictors of this event, document behavior and activity associated with this period, and attempt to explain the increased risk of bear-caused human injuries in this period. We analyzed global positioning system (GPS) location and activity data from brown bears in south-central Sweden, using generalized linear mixed models, statistical process control, and activity analyses. Bears arrived at their den sites between 6 October and 1 December. Timing varied by reproductive category, bear age, and year. Half of all bears significantly reduced their activity before arriving at the den area: on average 2,169 m away from the den and 1.8 days before arrival. The other half reduced their activity after arriving at the den area. The latter bears took longer time to reach hibernation activity levels, but we did not find a difference in the start date of hibernation between the 2 groups. Bears also appeared to be sensitive to disturbance in this period, with higher den abandonment rates than later in winter, particularly for males and for bears that had not visited their den sites previously. Den entry occurred from October to December, with high variability and poor predictability of its timing. Therefore, restricting hunting or other recreation activities to reduce risk of injury by bears and disturbing bears probably would be both impractical and ineffective. Our findings can be used to educate hunters about bear behavior at this time of year. Many people associate dens with an increased risk of a bear responding aggressively to disturbance to defend its den, but our results indicate that other behavioral, and possibly physiological, changes in this period also may be involved. © 2014 The Authors. The Journal of Wildlife Management published by The Wildlife Society.

Human development and climate affect hibernation in a large carnivore with implications for human–carnivore conflicts

“…Sahlén et al. () and Friebe et al. () both reported that older brown bears arrived earlier to their dens.…”

“…We calculated hibernation start and end dates using activity data from GPS collars (Friebe et al, 2014;Gervasi, Brunberg, & Swenson, 2006;Laske, Garshelis, & Laizzo, 2011;Sahlén, Friebe, Səebø, Swenson, & Støen, 2015). When we successfully determined both dates for a bear over a winter, we also calculated the duration of hibernation.…”

Physiological reactions to capture in hibernating brown bears

“…We previously reported that capture of hibernating brown bears resulted in den abandonment in 12 (92%) of 13 captures, compared with 22% overall den abandonment rate in the study area (Sahlén et al ., 2015). Although we do not know of other reports of the effects of capture on denning brown bears, a study reporting the capture of 14 hibernating female American black bears with cubs found that none abandoned their dens (Doan-Crider and Hellgren, 1996); others have reported that capture or approach of black bears during denning resulted in den abandonment rates of 17% (Tietje and Ruff, 1980) and 29% (Goodrich and Berger, 1994).…”

“…Although abandoned dens were documented to be more frequently located closer to plowed roads (Elfström and Swenson, 2009), the physical characteristics of the denning site did not differ dramatically between successful and abandoned dens (Elfström et al ., 2008). In Sweden, den abandonment rates are high, with 9% (of 194 bear winters followed by VHF telemetry; Swenson et al ., 1997) and 22% (of 90 followed by the more accurate GPS technology; Sahlén et al ., 2015) changing their dens. Although the later study found no gender differences, pregnant adult females that changed dens had significantly greater cub mortality than those that did not abandon dens (60 vs. 6% lost at least one cub at the den or shortly after leaving it).…”

“…Some authors have reported that both brown and black bears are more susceptible to den abandonment following disturbance earlier in the denning period than later (Tietje and Ruff, 1980; Beecham et al ., 1983; Smith, 1986; Kolenosky and Strathearn, 1987; Swenson et al ., 1997; Sahlén et al ., 2015). Most disturbed bears redenned (Kolenosky and Strathearn, 1987; Hellgren and Vaughan, 1989) and even successfully had cubs (Smith, 1986), although in some cases the cubs died following den abandonment (Elowe and Dodge, 1989; Goodrich and Berger, 1994).…”