Selection of Den Sites and Chronology of Hibernation by Black Bears in the Eastern Sierra Nevada and Western Great Basin
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Authors
Long, Morgan E.
Issue Date
2023
Type
Thesis
Language
Keywords
American black bears , den-site selection , Great Basin , hibernation , Sierra Nevada , Ursus americanus
Alternative Title
Abstract
Hibernation is a common adaptation in many species of animals, which allows them to conserve energy during the winter while access to food is limited. Hibernation is especially important for American black bears (Ursus americanus); both for energy conservation and reproduction because parturition occurs while females are occupying their dens. Across the species’ range, however, denning strategies may change as a result of habitat loss and climate change, and selection of suitable den sites may be an important behavior with implications for reproductive fitness. Black bears in Nevada are distinct from other populations of bears because of their adaptations to an arid environment, and the land use history of the mountains surrounding Lake Tahoe; making this an important population to understand denning behaviors. Our objectives were to identify: 1) which physical characteristics influenced selection of den sites and 2) which environmental factors influenced timing of entrance and exit of dens between females and males. We evaluated selection of den sites by black bears at two spatial scales in the eastern Sierra Nevada and western Great Basin from 2011-2022. When compared with available sites within 300-m from each den site, bears selected dens with a high level of concealment, high canopy cover, and rugged terrain. When compared with available sites within 300-1000-m from each den site we did not see selection based on landscape characteristics. Females remained in the dens longer than males by entering earlier in the autumn and exiting later in the spring. We did not observe differences in timing of entrance into or exit from dens among years, and overall did not find correlations between timing of entrance or exit with either snow depth or temperature. Knowing what characteristics are important for selection of den sites, and what, if any, factors may influence timing of denning, helps us understand how this species may be adjusting to environmental changes and how black bears are using resources across the landscape.