Island foxes interact with their habitats in ways that illustrate the near-optimal conditions of the environments in which they live. Foxes utilize nearly all available animal and plant resources, so there is ample food, and nearly all vegetation communities on the islands provide at least marginal if not high-quality habitat. Foxes adapted to the natural absence of predators by acquiring more diurnal (daytime) behavior patterns, and the combination of plentiful resources and tolerance for high population densities make foxes less inclined to disperse great distances in comparison to other species. This chapter examines the food habits, foraging behavior, habitat requirements, and dispersal tendencies of island foxes in wild populations.
Like other members of the genus Urocyon, island foxes are omnivorous, utilizing both plant and animal material in their diets (Moore and Collins 1995). Deer mice (Peromyscus maniculatus ssp.) are the most common animal prey taken by island foxes. Deer mice are present on all of the islands, and are the only native rodent on Santa Rosa, San Miguel, and San Nicolas. On San Miguel, the percent occurrence of mice in fox scats in several studies ranged from 10% to over 90% across all seasons (Collins 1980, Crowell 2001). Although mice are a common prey item, the quantity of mice in fox diets does not necessarily reflect mouse availability. Mouse abundance is highest in the summer and fall, following spring reproduction, and low in the winter and early spring due to winter mortality.