[Illustration: FIG. 24. The approximate length of stay of each known occupant of a den that was examined six times in the winter of 1955-1956 at the Damm Farm. Most of the occupants used the den as a temporary shelter and sought permanent hibernacula elsewhere. One turtle left the den for approximately two weeks and then returned to it for the rest of the winter. The temperature of the air outside the den (A) and the average body temperature of turtles in the den (B) are given at the bottom of the diagram for each date the den was examined. The symbol "J" represents a juvenal turtle.]
In general, body temperatures approximated the temperature of the soil around the turtle. Body temperatures tended to be slightly higher than soil temperatures in November and December but were slightly lower than soil temperatures in the months of February and March. The lowest body temperature recorded for any turtle that survived a winter was 2.7 degrees, taken from an adult female on December 26, 1955. Body temperatures one to three degrees higher were common in the coldest part of the winter. Turtles in shallow hibernacula, like those observed in wooded areas at the Reservation, are probably subjected to freezing temperatures at least for short periods but I have no records of body temperatures this low, except where they were induced experimentally. Turtles exposed to temperatures of zero degrees or slightly lower would retain enough heat to survive without freezing for a period of several hours or even a day if well insulated. A temperature gradient exists within the body; cloacal temperatures, for example, differ from temperatures deep in the colon and temperatures in the dorsal and ventral parts of the body cavity (taken by manipulating the bulb of the thermometer while it was in the colon) differ from one another. Probably, therefore, some parts of some turtles--probably the top of the shell or the extremities--freeze in winter without causing the death of the turtle. Ewing (1939:91) found a female of _T. carolina_, just emerging from hibernation, that had lost some scutes from its carapace; he found the missing scutes in the hibernaculum and attributed their loss to severe temperatures in the winter of 1933-34.