Fig. 23. Changes in temperature of the body of four juvenal (nos. 1 to 4) and five adult individuals of T. o. ornata (nos. 5 to 9) exposed to a constant air temperature of zero degrees Centigrade for periods of 100 and 200 minutes, respectively. The vertical arrows indicate when the turtles were removed to an air temperature of 27 degrees. Sizes and weights of the turtles used are given in the text. Turtle number nine, a female, was killed by means of chloroform before experiment began. Rate of change in temperature in specimens was inversely proportional to size. All turtles survived the experiment.
Hibernating turtles and those experimentally chilled were usually comatose but were almost never completely incapacitated even at temperatures at or near zero degrees. Experimental pinching, probing, and pulling revealed that muscles operating the neck, the limbs, and the lobes of the plastron could be controlled by the turtle at low temperatures; hissing, resulting from rapid expulsion of air through the mouth and nostrils (when the head and limbs are drawn in reflexively) occurred at all body temperatures but was sometimes barely audible in the coldest turtles. Of all living turtles observed, only two (hatchlings 1 and 2 in coldroom experiment) were completely immobile at low temperatures, failing to respond even to pinpricks at body temperatures of 0.8 and 1.7 degrees, respectively, although other turtles, under the same experimental conditions, consistently gave at least some response to the same stimulation.
Turtles chilled experimentally continued to move about voluntarily, albeit sluggishly, at temperatures much lower (2.5° for each of four adults; 10.0° and 6.2° for two juveniles) than those at which locomotion was resumed in the warming phase (13° for the adults, 21.7° and 20.1° for the juveniles). Hatchlings chilled so rapidly that it was difficult to ascertain accurately the temperature at which inactivity was induced. Juveniles became active gradually, moving slowly about when the body temperature reached approximately 20 degrees but not attempting more strenuous activities such as climbing the walls of enclosures, until body temperatures of 22 to 25 degrees were attained. Adults, on the other hand, exhibited "normal" activity as soon as they became voluntarily active.
The ability of ornate box turtles to move about when the body temperature is near the lethal minimum probably enables those caught in the open by a sudden drop in environmental temperature to find cover that keeps them from freezing to death. Prolonged chilling, on the other hand, seems to create a physiologically different situation; the temperature at which activity is resumed is higher and subject to less variation.
Juveniles were more rapidly affected by environmental temperatures, were subject to different thresholds, and were inactive over a wider range than were the adults. Indeed, the rate of chilling, rather than absolute body temperature alone, might in large measure influence the reactions of turtles to environmental temperatures. If this be so, smaller turtles, having a narrower thermal range of normal activity, must lose at least some of the advantages gained by their ability to warm up more rapidly.
Hatchlings and juveniles at the Damm Farm were always active on days when at least some adults were also active. Fitch (1956b:466) found that, in northeastern Kansas, species of small reptiles and amphibians are active earlier in the season than larger species and that the young of certain species become active earlier than adults. Fitch stated, "… small size confers a distinct advantage in permitting rapid rise in body temperature by contact with warmed soil, rock or air, until the threshold of activity is attained"; he pointed out also that young animals, if able to emerge earlier than adults, would benefit from a longer growing season. Hatchlings and juveniles of T. ornata would benefit greatly from an extra period of activity of say, one or two weeks in spring and a similar period in autumn, especially if food were plentiful. The extra growth realized from such a "bonus" period of feeding would significantly increase the chance of the individual turtle to survive in the following season of growth and activity.
Ornate box turtles are active within a narrower range of temperatures than are aquatic turtles in nearby ponds and streams of the same region. Observations by William R. Brecheisen and myself on winter activity of aquatic turtles indicate that, in Anderson County, Kansas, the commoner species (Chelydra serpentina, Chrysemys picta, and Pseudemys scripta) are more or less active throughout the year; although they usually do not eat in winter, they are able to swim about slowly and in some instances (P. scripta) even to carry on sexual activity at body temperatures only one or two degrees above freezing. But, ornate box turtles hibernating in the ground a few yards away are incapable of purposeful movement at such low body temperatures.
HIBERNATION
In northeastern Kansas ornate box turtles are dormant from late October to mid-April—approximately five and one half months of the year. Individuals may be intermittently active for short periods at the beginning and end of the season, however. Once a permanent hibernaculum is selected dormancy continues until spring; unseasonably warm weather between mid-November and March does not stimulate temporary emergence. There is little movement during dormancy except for the deepening or horizontal extension of the hibernaculum.