McNab’s habitat productivity hypothesis predicts that animals’ energetic needs and home range size correlate positively. Although much support exists for his hypothesis, a paradox emerges when the two correlate negatively, which occurs occasionally. One case is snowshoe hares in the Adirondacks, who we found to have larger summer home ranges (mean = 47.9 ha) than winter home ranges (mean = 27.6 ha). Herbaceous vegetation in summer provides plentiful nutrients while woody browse in winter has fewer nutrients. Therefore, we expected summer ranges to be smaller than winter home ranges in concordance with McNab’s hypothesis. In an effort to isolate a mechanism for the observed paradox, we examined hares’ moves on two spatial scales: home ranges and individual moves. Snowshoe hares offer a good model system to explore this paradox as hares respond primarily to only 2 factors: predation risk and browse needs, both of which are functions of surrounding vegetation. We radio-tracked and snow tracked snowshoe hares. Home ranges were estimated by the kernel density method. Individual moves were quantified from snow tracking. Habitat characteristics from snow tracks were compared to random locations in hare habitat to determine if hares respond the vegetation.
Results/Conclusions
On average, 62.8% of the winter home range area was placed in coniferous stands, while 59.3% of summer ranges occurred in hardwood stands. Hares had a mean inter-seasonal movement distance of 673 m. As many as 6 hares overlapped their home ranges, each home range overlapped each of the other hare’s home ranges in winter (mean = 40.3%) and in summer (mean overlap = 12.3%). On the smaller spatial scale of individual moves, preliminary analysis of backtracking data has not shown that hares select browsing or traveling microhabitat in response to canopy cover at 0, 5, and 10 m; or shrub cover at 5 or 10 m. Because the effects of surrounding habitat on moves may not explain the paradigm, we will measure move rates (as inter-track distance) and giving up densities (as twig diameter and percent of browsed tips) to try to isolate a mechanism for the paradigm.
