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Grizzly bear use of avalanche chutes in the Columbia Mountains, British Columbia Ramcharita, Roger Karim

Abstract

I examined spring season use of avalanche chutes by grizzly bears (Ursus arctos L.) in the Columbia Mountains, southeastern British Columbia. Sixty radio-collared grizzly bears were monitored between 1994 and 1998. The frequency of avalanche chute use, the selection of general habitat characteristics within avalanche chutes, and the selection of specific feeding and bedding sites within avalanche chutes by grizzly bears were documented. Fifty-four percent (366/672) of all grizzly bear radio-locations during the spring season (May 1 to July 31) were in avalanche chutes. The proportion of radio-locations in avalanche chutes for the 37 grizzly bears that accounted for > 10 spring season radiolocations each ranged between 20% and 90% (x = 56% ± 18% [mean ± SD]). This variation was not attributable to differences in use between sex or age classes. Within avalanche chutes, grizzly bears selected east and south aspects and areas dominated by grasses and forbs with minimal shrub abundance. Grizzly bears avoided very steep slopes but used all elevational parts of avalanche chutes - upper start zones, tracks, and lower runout zones. These patterns appeared to be tied to feeding site selection, because evidence of feeding was found at most telemetry locations investigated on the ground. Grizzly bears selected feeding sites on the basis of forage value and visual cover. Most feeding sites were characterized by high forage value and low visual cover, but weak positive interaction between these two factors indicated that grizzly bears also selected feeding sites with slightly lower forage values but high visual cover. Bed sites were found both in forest adjacent to avalanche chutes and directly within avalanche chutes. All bed sites found in forests adjacent to avalanche chutes were < 25 m from the forest / avalanche chute edge. The impact on grizzly bear use of avalanche chutes by two timber harvest activities was also examined. Grizzly bears avoided areas within avalanche chutes that were adjacent to cutblocks, possibly due to the removal of escape cover. In contrast, grizzly bears selected areas close to logging roads. Most logging roads traversing avalanche chutes in the study area had minimal vehicle traffic and were often situated close to areas with abundant food resources. I present suggestions for managing this important spring season habitat for grizzly bears.

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