Cowles and Bogert (1944:277) determined optimum levels of body
temperature of desert reptiles by averaging body temperatures falling
within the range of normal activity; they defined this range as, "...
extending from the resumption of ordinary routine [activity] ... to
... a point just below the level at which high temperatures drive the
animal to shelter." Fitch (1956b:439) considered optimum body
temperature in the several species that he studied to be near the
temperature recorded most frequently for "active" individuals; he
found (_loc. cit._) that of body temperatures of 55 active _T.
ornata_, 66 per cent were between 24 and 30 degrees, and that the
temperatures 27 and 28 occurred most frequently. Fitch concluded (_op.
cit._:473) that the probable optimum body temperature of _T. ornata_
was 28 degrees and that temperatures from 24 to 30 degrees were
preferred. Although Fitch treated all non-torpid individuals that were
abroad in daytime as "active" and did not consider the phenomenon of
basking, his observations on optimum body temperature agree closely
with my own.
Body temperatures of 153 box turtles that were known definitely to be
active, ranged from 15.3 to 35.3 degrees. The mean body temperature
for active turtles was 28.8 degrees (A+- 3.78[sigma]) (Fig. 22).
Ninety-two per cent of the temperatures were between 24 and 30 degrees
and 50 per cent were between 28 and 32; temperatures of 29 and 30
degrees occurred most frequently (22 and 21 times, respectively). The
ten body temperatures below 24 degrees all were recorded before 9 A.
M. on overcast days when the air was cool and humid. It is noteworthy
that two of these low temperatures (18.8A deg. and 19.0A deg.) were from a
copulating pair of turtles; two others (21.8A deg. and 22.0A deg.) were from
individuals that were eating. The highest temperature (35.3A deg.) was from
a large female that was feeding at mid-morning in a partly shaded
area.
The mean body temperature for active individuals (Fig. 22) is probably
somewhat below the ecological optimum, because a few temperatures were
abnormally low. The large number of body temperatures in the range of
29 to 31 degrees indicates an optimum closer to 30 degrees. Optimum
body temperatures may vary somewhat with the size, sex, or individual
preference of the turtle concerned.