Denning Behavior of Black Bears in Boreal Forest of Alberta

Abstract

Denning chronology and behavior of black bears (Ursus americanus) were investigated in east-central Alberta. Twenty-eight instrumented bears were monitored from fall through spring in 197576 and 1976-77. Adult males exhibited significantly longer movements to den sites than other cohorts. Bear dens usually were located on the periphery of summer ranges or beyond. Bears selected mixed stands of mature aspen (Populus spp.) and spruce (Picea spp.), or mature spruce stands for den sites. Muskeg was avoided. All but 2 dens were excavated beneath ground level or under rootmasses of fallen trees. All chambers were lined with grasses and litter from the immediate proximity of the den. Observed periods of den construction ranged from 5 to 10 days. Bears entered their dens during a 4-week period starting 7 October in 1975 and during a 5-week period starting 1 October in 1976. Delayed denning in 1975 was attributed to the abundance of blueberries (Vaccinium spp.) that persisted into fall. Denning dates varied among bear cohorts; adult females and subadults denned first and adult males last. The average overwinter weight loss of 11 bears without offspring was 16%. The energy demands of nursing offspring (N = 1 bear) or den abandonment (N = 4 bears) each accounted for an additional 9% overwinter weight loss. Time of emergence from dens spanned the 1st 2 weeks of April in both years. Adult males emerged first and females with cubs last. Females with offspring (i.e., females with cubs or yearlings) remained in the vicinity of dens for an average of 17 days (9-23 days) after emergence, whereas bears without offspring (i.e., adult males, subadults, and barren females) did so for an average of 7 days (2-13 days). J. WILDL. MANAGE. 44(4):858-870 The location and structural characteristics of black bear dens vary among regions. In Michigan, dens are located beneath logs or stumps, or excavated into hillsides (Erickson 1964). Rogers (1970) found that most black bears in northeastern Minnesota select bulldozed piles of logs, brush, or soil for den sites. Others excavate dens beneath boulders, stumps, windfalls, or tree roots. Most black bears in Montana den in hollow trees, but also use fallen logs, rock caves, and hillside excavations (Jonkel and Cowan 1971). In North Carolina, bears den in hollow trees or nestlike structures on the surface of the ground (Hamilton and Marchinton 1980). The purpose of this paper is to describe the denning chronology and behavior of black bears in the boreal forest of eastcentral Alberta. Although the boreal forest in Canada comprises the largest continuous area of black bear habitat in North America, information on bear denning behavior there is limited. Such data are of value for species management and for the assessment of impacts associated with the development of 43,700 km2 (Nicholls and Luhning 1977) of Alberta Oil Sands during the next decade. Thanks are due B. Pelchat, B. Young, T. Kemp, C. Ballweg, and S. Tietje for field assistance. Financial support was provided by the Alberta Department of Energy and Natural Resources (Fish and Wildlife Division), the National Science Foundation (Grant BMS75-09816), the Research Committee of the Graduate School, University of Wisconsin, and Gulf Canada Resources, Inc.