The racer's annual cycle of activity is, of course, controlled primarily by the weather, and is much delayed or accelerated in some years. But certain stabilizing factors cause the racer's annual cycle to be less variable than that of the weather. For example, in spring when persistently cool weather delays emergence from hibernation beyond the normal time, the increasing azimuth of the sun, and more intense sunshine cause the soil to warm, despite low air temperature, until emergence is finally triggered. Having once emerged, the racer is able to control its bodily temperature to a large extent by basking in sunshine to gain warmth, or by seeking shade or underground shelter to escape overheating. By such behavioral thermoregulation extremes of weather are neutralized, or at least buffered to some degree.
Fig. 4. Yearly variation in catch of blue racers along hilltop outcrop in autumn on the Reservation and Rockefeller Tract, grouped in same ten-day intervals indicated for [Fig. 3].
In the course of my study no racers were found in their actual hibernacula. Insofar as known, these were always in deep crevices in strata of limestone near hilltops, and were inaccessible except by removal of the solid rock. The crevices where racers hibernate are known to be several feet deep in some instances, extending well below the frost line. Periodic temperature readings in two such crevices at depths of 12 inches and 30 inches, taken in the winter of 1954 (Fitch, 1956:471) showed that temperatures during dormancy are usually well within the range 0°C to 10°. Whether the racers congregate in hibernating masses in regular "dens" on the Reservation has not been definitely determined, but if so, most of the hibernating groups must be small, because those trapped along the ledges are well scattered, and, in fact, give the impression of being rather uniformly distributed along them. However, ledges of northward exposure are not used as hibernation sites, so far as known, and those of full southward exposure are perhaps preferred, especially where the hilltop has a southward projecting spur, and the exposed rock face is extensive, with many cracks and fissures. I have been unable to detect differences in types of hibernation sites preferred between the racer and the copperhead, which is somewhat more numerous on the same area.
Several authors have contributed to knowledge of hibernation in the racer. Boyer and Heinze in Missouri (1934:195) noted that blue racers often were associated with copperheads in the vicinity of places chosen for hibernation. Burt (1935:329) in Kansas found blue racers emerging from dens among rocks on a prairie hillside, associating with other snakes, Diadophis punctatus, Elaphe guttata, and Pituophis melanoleucus. In the Chicago region, Pope (1944:173) reported scores of blue racers aggregating in October on and around a sand dune with oak woodland. In Ohio, Conant (1938:55) found three blue racers hibernating together about three feet underground in a small hole. One found at another locality had apparently hibernated in company with a massasauga (Sistrurus catenatus). In Maryland Cohen (1939:137) saw racers (C. c. constrictor) in the act of emerging from an old vole burrow that was a communal hibernaculum, on April 6, 8, and 10. Air temperatures at the time of emergence were 12.5° and 18.5° Centigrade. In Illinois, Schroder (1950:1-2) found seven blue racers hibernating in masses, intertwined with each other and with bull snakes at depths of 36 inches and 42 inches in an abandoned mammal burrow in a sand dune area in early February.
Fig. 5. Bodily temperatures of blue racers kept in a large outdoor enclosure and checked from time to time when they were active and the sun was shining, in June and July, 1962.
In the course of routine field work I often carried a Schultheis quick-reading thermometer, and from time to time I had opportunities to take the body temperatures of blue racers newly captured by hand. The trend of these records indicated the temperature range within which the snakes normally limit their activity, and the preferred temperature. In an earlier publication (Fitch, 1956:459-460) based on a few more than half the number of records of temperature now available, I discussed responses of the blue racer to temperature. The newer data bear out the trends previously revealed; of 60 records, 39 are within the six-degree range from 29° to 35°, and records are most concentrated in the one-degree range, 34° to 35°. Racers were found active at air temperatures between 15.5° and 32.4°, with the greatest concentration between 26° and 27°. Compared with most other kinds of North American snakes, the racer is remarkably tolerant of heat, and often is several degrees warmer than the level that those of other genera will normally tolerate. Racers have been seen crawling in the sunshine, or basking on days that were uncomfortably hot for humans. For example, on August 28, a large female racer released from a trap was followed and her behavior observed; after crawling some 50 feet through the grass she climbed from a ditch bank onto sunflower stalks and elm saplings, and came to rest among the stalks, in a spot strategically situated for catching grasshoppers. More than half her body was exposed to sunshine and air temperature was slightly above 34° Centigrade, yet the snake showed no sign of discomfort, and for the several minutes that she was kept under observation, did not attempt to withdraw into the shade.