Niche dimensions of New England cottontails in relation to habitat patch size.

We examined physical condition, niche dimensions, and survival of New England cottontails (Sylvilagus transitionalis) that occupied 21 habitat patches of different sizes during winter. Rabbits on small patches (≤2.5 ha) were predominantly males, and both sexes had lower body mass than individuals on large patches (≥5.0 ha). Niche indices (β, where β ranges from 0 to 1. and values approaching 1 indicate generalized resource use) of habitat use revealed that rabbits on small patches used a greater variety of microhabitats (based on understory stem density: β, and proximity to cover: β) than rabbits occupying large patches (β=0.65, β=0.66). Rabbits on small patches also consumed low quality forage more often and fed at sites farther from escape cover than rabbits on large patches. There were no significant correlations between rabbit densities and niche dimensions. Niche expansion was not a result of compertitive release or relaxation of predator pressure. Rabbits on small patches apparently modified their niche dimensions in response to resource limitations. This response included occupying sites with limited understory cover that apparently resulted in rabbits on small patches having a lower survival rate (0.35) than rabbits on large patches (0.69) during a 10-week monitoring period. Skewed sex ratios and low survival rates among rabbits on small patches suggest that these habitats act as sinks to dispersing, juveniles from large (source) patches. As a result, local populations of New England cottontails may become vulnerable to extinction if larte patches of habitat are not maintained.