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Effects of Roads on Black Bear Distribution in Southern Vermont
Drasher, Caitlin E.
Drasher, Caitlin E.
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Abstract
The American black bear (Ursus americanus) is a wide-ranging, large carnivore species that makes use of multiple habitat types throughout the year. In the northeastern US, black bears require large areas of relatively undisturbed forest and avoid development, such as urban and suburban areas. Roads represent another form of development that may affect the distribution of bears. However, the effects of roads remain largely unknown and represent a potential conservation concern. We sought to determine the relationship between roads and distribution of black bears in a forested region of southern Vermont. We examined the probability of occurrence of black bears using GPS-collar data (n = 30,179 locations) collected from a marked population of bears (n = 8 females, 15 males) from 2011 to 2014. We then constructed a set of 7 candidate models to explain occupancy that included combinations of three road types: secondary, vehicular, and local. Model selection techniques were used to determine the best model in the set. Models were performed separately for male and female bears, which have been shown to exhibit different distribution patterns elsewhere. The top model for each sex was the most complex in the set, and included the additive combination of all three road types. For males, vehicular and local roads positively affected occupancy, whereas secondary roads had a negative influence on occupancy. For females, vehicular and secondary roads positively affected occupancy, whereas local roads negatively affected occupancy. Our results indicate that small, low traffic, residential and ATV roads influence bear distribution; most likely by providing easy pathways to travel through the forested landscape and food resources not found elsewhere. Secondary and local roads also affect sexes differently, which could result in demographic and genetic consequences. Models provide a measure of the effect of different roads on bear distribution that can help inform decision-making about development in the forested landscapes of Vermont.
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2017-01-01
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Drasher_Thesis.pdf
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