Date of Award
Level of Access Assigned by Author
Master of Science (MS)
Wildlife Ecology and Wildlife Conservation
Daniel J. Harrison
Second Committee Member
William B. Krohn
Third Committee Member
Robert S. Seymour
Snowshoe hares (Lepus americanus) respond to seasonal changes in vegetation in the northern and western portions of their range. During winter, hares use dense conifer stands that may provide thermal and predatory refugia, then during summer move to areas with more herbaceous food and cover. These movements influence hare demographics, with greater survival rates corresponding to seasonal use of dense, primarily coniferous stands. Different harvesting practices in commercial forests produce vegetative communities that may support differing hare densities among forest stand- types between seasons, but seasonal use of habitat had not been documented in northern Maine on a large spatial and temporal scale. In response to spatio-temporal availability of hares, the U.S. federally threatened Canada lynx (Lynx canadensis) may shift their resource selection. Though lynx may be relatively less specialized on snowshoe hares in mid- and southwestern regions of their range, their degree of dietary specialization had not been quantified in Maine.
In Chapter One, I investigated whether snowshoe hare pellet densities were different between two seasons across three forest stand-types: regenerating (RG) coniferous- dominated (19-39 years post-harvest), selection harvested (SEL) mixed coniferous- deciduous (8-18 years), and mature (42-80 years). I then determined what vegetation characteristics most strongly influenced hare densities between seasons across 26 forest stands. I evaluated 17 candidate models using generalized linear mixed models and standard model selection techniques.
Hare densities, indexed by pellet densities, were measured semi-annually in 41 stands from 2005-2012. Densities were significantly higher during leaf-off (winter) than leaf- on (summer) periods in RG stands, but not in mature or SEL stands. Pellet densities were greater in RG than other stand-types during both seasons, and unexpectedly, significantly higher during the leaf-on season. These results suggest greater winter survival or movement to RG from summer to winter, and relatively higher summer survival and juvenile recruitment in RG. Seasonal differences in pellet densities across 26 stands were most strongly influenced by conifer sapling density [68% relative importance weight (RIW)] and total sapling density (11% RIW). During the leaf-off season when snow may interact with vegetation, the strongest influence on pellet densities was percent understory coverage of all conifer foliage (RIW 88.9%).
In Chapter Two I examined whether lynx shift their food habits at the southeastern limit of their range. I documented food habits using scats genetically confirmed as lynx during a summer-lower (2007-2012, 0.92 hares/ha, n=199 scats) and a winter-higher hare density period (2001-2006, 1.98 hares/ha, n=125). The summer-low had greater dietary breadth than winter-higher hare density period (F4,322=0.0068, 1000 randomizations). Frequency of occurrence of hares in food item categories declined during summer-low (75.2%, n=230 food item categories) compared to winter-high hare density period (92.1%, n=127). I suggest increased relative availability and accessibility of rodents and birds promotes diversification of lynx diets during the summer-low. Greater use of hares during both seasons and across periods of changing hare density indicated lynx specialize on snowshoe hares at the southeastern limit of their geographic range, although lynx broaden their dietary niche when relative availability of alternative prey increases.
Olson, Sheryn J., "Seasonal Influences on Habitat Use by Snowshoe Hares: Implications for Canada Lynx in Northern Maine" (2015). Electronic Theses and Dissertations. 2273.