Black bear resource selection in the northeast Cascades, Washington
Introduction
Once found ubiquitously and in relatively high numbers across North America, American black bear (Ursus americanus) populations have become increasingly isolated (Poelker and Hartwell, 1973, Pelton, 1982, Hummel and Pettigrew, 1991). Human-caused mortality and loss or alteration of habitat are two of the most significant reasons for the historical decline of bear populations (Morrison et al., 1992, US Fish and Wildlife Service (USFWS), 1993). Because adequate habitat is a primary requirement for survival of wildlife populations (Morrison et al., 1992), wildlife managers need to determine the relationships between a species and its habitat to develop appropriate management strategies. As such, numerous scientific studies have focused on the ecology, including habitat relationships, of the American black bear, throughout much of its range (Jonkel et al., 1971, LeCount, 1982, Kasworm and Manley, 1988, Unsworth et al., 1989, Beck, 1991, Hellgren et al., 1991, Schwartz and Franzmann, 1991).
In contrast, very little research has been conducted on the black bears of Washington State, particularly on those populations inhabiting the east side of the Cascade Mountains. Black bears in Washington are being managed without site-specific information (WDFW, 1996) and several state and federal agencies are working to remedy this situation (Gold, 1997, Washington Department of Fish and Wildlife (WDFW), 2001). Mace and Jonkel, 1983, Weaver et al., 1996 recognized that neighboring populations of bears can exhibit different habitat use. Therefore, to effectively manage and conserve black bears in an environment of increasing human encroachment and resource demands (Miller, 1990), accurate information on specific habitat requirements is critical (Schoen, 1990, Clark et al., 1993, Manly et al., 1993).
As bears search for resources, they are responding to a variety of cues and experience in using a combination of habitats in a usually heterogeneous landscape. Habitat selection is a continuum that Johnson (1980) segregated into hierarchical levels, such as selection of a home range within a study area (2nd Order resource selection), or selection of foraging components within that home range (3rd Order resource selection). Analyzing habitat selection at multiple levels can allow for observation of influences that may be masked within a single-level analysis. Our objective was to provide a detailed description of annual black hear habitat selection in the northeast Cascades of Washington State at the 2nd and 3rd Orders of resource selection.
The study area ranged from slightly west of the Cascade crest, near Ross Lake, east to the Sinlahekin River valley, and from the Canadian border, at its junction with the Pasayten River, south to the Twisp River. The majority of the land (69%) was administered under the Okanogan National Forest, 39% of which was designated as the Pasayten Wilderness Area. The landscape in the study area varied from dry, lowland valleys, to wet, alpine meadows, with elevation ranges from 500 m in the valleys, to peaks exceeding 2700 m. The study area boundary was delineated to encompass all movements of this collared black bear population. Because bears are wide-ranging and mobile (Schoen, 1990) we created a conservative study area boundary to prevent elimination of possible bear movement. The boundary was then delineated along general geographical boundaries, i.e. ridges, lakes, etc. The study area encompassed approximately 7800 km2 and a general diagram is presented in Fig. 1. Precipitation ranged from 21 to 406 cm, falling mostly as snow. Road densities ranged from 0 to 2.7 km/km2, within bear home ranges.
The major vegetation zones consisted of ponderosa pine (Pinus ponderosa), grand fir (Abies grandis), Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), lodgepole pine (P. contorta) and subalpine fir (A. lasiocarpa) (Gaines et al., 1994, p. 2). Shrub steppe types were also prominent. Shrub fields and meadows were interspersed throughout the study area. In 1994, two large fires burned approximately 52.4 km2.
Section snippets
Telemetry
Black bears were trapped/captured with Aldrich leg snares or from a helicopter from 1994 to 1996. Captured black hears were immobilized, examined, marked with plastic ear tags and a lip tattoo, fitted with a radio collar and released (Koehler et al., 2000).
We tracked radio-collared bears from den emergence to den entrance in 1995 and 1996. Radio-collared bears were located from the air in a Cessna 182 TRG fixed-wing aircraft. After each flight, we transferred all bear relocations from flight
Results and discussion
Eleven female and 26 male bears were radio-collared. We used data from 26 of the black bears in subsequent analyses, for a total of 1916 relocations. The number of relocations for these 26 bears ranged from 24 to106 (mean=73.6, S.E.=4.75). The remaining four bears were excluded because of low numbers of relocations.
We collected data for 46 test collars. Telemetry error distances ranged from 5 to 1430 in, with a mean of 226 m. The distribution of our telemetry error distances displayed strong
Conclusion
Our multi-scale analysis suggests black bears select for different habitats at different scales. Black bears may select home ranges based on habitat classes with better food availability, such as riparian forests and meadows. Within their home range, bears may be selecting for a mosaic of food resources and the security of forested habitat classes.
Riparian and mesic sites, with diverse and abundant food resources, are important to black bears in the northeastern Cascades. The dry climate of the
Acknowledgements
Funding was provided by the US Forest Service, Okanogan and Wenatchee National Forests, and the Washington Department of Fish and Wildlife. Fieldwork, technical assistance and manuscript editing were provided by G. Koehler, R. Naney, D. Munzing, G. Holser, J. Almack, S. Fitkin, T. Radandt, H. Carriles. D. Pletscher. R. Callaway, R. Perrow, W. Kasworm, J. Haberberger, W. Hart, F. Hovey and D. Houston.
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