Natural History of the Ornate Box Turtle, Terrapene ornata ornata Agassiz

by John M. Legler

The following observations, extracted from field notes, indicate that body temperatures near 40 degrees are the approximate lethal maximum and are well above those temperatures voluntarily tolerated by T. ornata. On July 4, 1955, a subadult female was in the water at the edge of a pond. The temperatures of the air, water, and turtle were 32.0, 30.6, and 30.2 degrees, respectively. At 11 A. M. the turtle was tethered in direct sunlight on the hard-baked clay of the pond embankment (temperature of air 33.4°). The turtle's response to steadily rising body temperature over a period of 31 minutes is illustrated by the following notes.

Time (A. M.)	Body temperature	Remarks
11:00	33.0	Tethered on slope.
11:05	34.6	Strains at tether in several directions.
11:09	36.5	Tries frantically to get away; draws in limbs and head rapidly and momentarily at any movement on my part, and hisses loudly.
11:13	37.5	Mouth held open slightly; turtle overturns in effort to escape; frantic scrambling resumed a few seconds after I right turtle.
11:17	38.2	Mouth now held open most of the time; white froth begins to appear around mouth.
11:20	38.6	Stops activities every 10 seconds or so, rests chin on ground and gapes widely; will still pull into shell when prodded with stick.
11:23	39.2	Still wildly active; continues to gape widely every few seconds.
11:27	39.4	Frothing at mouth profusely.
11:30	39.6	Attempts to escape are now in short feeble bursts. Turtle released; crawls toward me and immediately seeks shade of my body; when I move off, turtle seeks shade of small isolated weed on pond embankment; turtle removed to damp earth at edge of pond.
11:35	39.5	Attempts to burrow into mud at edge of pond.
11:36		Enters shallow water and moves slowly back to shore.
11:37	38.8	Turtle thrown into center of pond where it remains motionless and drifts with wind to opposite shore; remains inactive in mud and shallow water at edge of pond; temperature of water near turtle 35.5.
11:57	35.0	Moves 50 ft. up slope to shade of low vegetation.
1:55 P. M.	32.5	Turtle has not moved.

The overheating may have incapacitated the turtle since it moved only 50 feet in the next two days; its body temperatures on the two days subsequent to the experiment were 26.8 and 20.6, respectively.

The mentioned gaping, as in higher vertebrates generally, cools the animal by evaporation from the moist surfaces of the mouth and pharynx. By keeping the mouth open for more than a few minutes at a time in hot dry weather, a turtle would surely lose body water in amounts that could not always be easily replaced. Ornate box turtles seem to utilize evaporation for cooling only in emergencies and rely for the most part on radiation and conduction to lower body temperature after reaching a relatively cool, dark retreat.

Box turtles were never active at body temperatures below 15 degrees and were seldom active at temperatures below 24 degrees. The two lowest temperatures (15.3° and 16.3°) were taken from individuals crossing roads on overcast days in early May.

In 78 box turtles that were under cover because their environmental temperatures were low, the body temperatures ranged from 2.7 to 30.6 degrees (mean 19.8 ± 6.38σ). The range of body temperatures in this group is greater than in the other groups shown in [Figure 22] because low body temperatures were studied over a wide range of conditions, including hibernation.

Box turtles actually seek cover because of low temperatures only in fall and spring and on occasional unseasonable days in summer when temperatures drop rapidly. Retreat to cover, in the normal cycle of daily activity, is governed usually by high temperatures at mid-day or by darkness at the end of the day. Turtles in dens, burrows, and grass forms, tended to burrow if temperatures remained low for more than a few hours.

Box turtles under cover where they cannot bask have little control over the lower range of body temperatures. The freezing temperatures of winter can be escaped by burrowing deeper into the ground. Temperatures approaching the lethal minimum, however, seldom occur during the season of normal activity. By remaining hidden in a burrow or den therefore, box turtles are fairly well protected from predators but are at a thermal disadvantage.

A number of turtles that had wet mud on their shells were found basking in early morning near ditches, ponds, and marshy areas; several others were partly buried in mud, shortly after daybreak, and another was at the edge of a pond after dark.