Mammals that favor forest habitat predominate within the Slide Wilderness. Among the 49 species known to exist there, black bears have done exceptionally well, as have snowshoe hare, gray squirrel and porcupine. White-tailed deer, who were successfully reintroduced into New York in 1887 via a protected habitat on lands now part of the wilderness area, winter here. Cottontail rabbit and beaver also maintain lower population levels. Fisher were reintroduced to the area in the late 1970s and have thrived in numbers significant enough to make life difficult for the porcupine, always abundant in the Catskills.