Every part of the 590-acre Reservation is used to some extent by blue racers living on this area. Home ranges of most individuals are so large as to include a variety of habitats, both woodland and grassland. The habitat preferences vary according to season. In autumn some racers migrating to rock ledges to hibernate are found in mesic forest, but at that time of year leaves have begun to fall and the forest floor is less dark and humid than in summer. In spring also racers not yet back on their summer ranges are often seen either along the hilltop ledges, or moving downhill through woods toward bottomland meadows. However, in summer, the finding of a racer in mesic woodland is a rare event. Occasionally the snakes make trips across such blocks of woodland hundreds of feet wide, but they do not linger in the woodland. In decreasing order of preference the habitats used by racers on my study area may be classified as follows: 1. Tall-grass prairie, (Plate 22) either original or regenerated, dominated by native perennial grasses in stands three feet to seven feet high, including big blue-stem (_Andropogon gerardi_), little blue-stem (_A. scoparius_) Indian grass (_Sorghastrum nutans_), and switchgrass (_Panicum virgatum_). 2. Pastureland, with introduced brome grass (_Bromus inermis_) and associated weedy vegetation. 3. Brush, in ravines, at woodland edge, and in riparian thickets. 4. Weedy fields, dominated by such pioneer plants as ragweeds, sunflowers, horseweed, milkweed, wild lettuce, aster and goldenrod. 5. Open type of woodland dominated by such trees as honey locust and osage orange. These habitat types are interspersed on the study area, and each racer has a wide choice of habitats without travelling beyond the limits of its own chosen area. Grassland that has been closely grazed, mowed or burned does not provide entirely adequate food or shelter, and under such conditions clumps of brush or other dense vegetation may be of critical importance. Throughout the racer's extensive range, fields of grain and hay at times provide suitable habitat, and may support large populations, but in spring, before the young cultivated plants have made much growth, or later in the season, after they have been cut, the racer may need to depend on adjacent areas of pasture, thicket, or woodland edge and the availability of such refugia to a large extent determines the numbers of racers on cultivated areas. Temperature Relationships