Determinants of home-range size of imperiled New England cottontails (Sylvilagus transitionalis) and introduced eastern cottontails (Sylvilagus floridanus)

In fragmented habitat, population persistence depends in part on patch quality and patch size relative to home-range size. The imperiled New England cottontail (Sylvilagus transitionalis (Bangs, 1895)) is an obligate user of shrublands in the northeastern United States, a highly fragmented and declining ecosystem. New England cottontail conservation efforts have targeted habitat creation; however, efforts are hindered by a limited knowledge of seasonal space use and its relationship to habitat quality, which could help inform minimum patch-size requirements and implications of competition with non-native eastern cottontails (Sylvilagus floridanus (J.A. Allen, 1890)). To address these uncertainties, we modeled home-range areas for both species as a function of season, patch size, sex, and two indicators of forage and cover availability. Home range was generally inversely correlated with measures of forage and cover resources and the response differed by season and species and did not vary with patch size. Instead, inclusion of matrix habitat within home ranges increased with decreasing patch size, placing individuals within smaller patches at a high risk of mortality. These risks may be mitigated in patches >7 ha and absent in patches >20–25 ha where predicted inclusion of matrix is lower or absent.

Foraging strategies of sympatric lagomorphs: implications for differential success in fragmented landscapes

In recent decades, the distribution of New England cottontails (Sylvilagus transitionalis) has declined substantially in response to forest maturation and fragmentation. Populations of eastern cottontails (Sylvilagus floridanus) have expanded into the range of S. transitionalis, since they are apparently less affected by the consequences of habitat modifications. We suspected that S. floridanus was able to exploit small patches of habitat where S. transitionalis was vulnerable to intense predation and we evaluated this explanation using large enclosures within which we manipulated the quality and distribution of food in relation to escape cover. In trials with low-quality food in cover and high-quality food in open areas, S. transitionalis sacrificed food quality for safety by remaining in close proximity to cover. Sylvilagus floridanus avoided low-quality food in cover and foraged at sites containing high-quality food away from cover. When food was removed from cover, S. transitionalis was reluctant to forage in the open and lost a greater proportion of body mass and succumbed to higher rates of predation than did S. floridanus. We applied these results to patterns of foraging by free-ranging rabbits in a fragmented landscape and estimated that S. transitionalis could successfully exploit only 32% of the available habitat without experiencing elevated rates of predation, whereas S. floridanus could exploit 99% of the habitat. Thus, the consequences of habitat fragmentation (especially higher predation risk) may not be as detrimental to S. floridanus, and this species will likely persist, whereas populations of S. transitionalis will continue to decline.