Temperature Variation in Free-Ranging Box Turtles (Terrapene carolina)

Joy M. Hester andMichael E. Dorcas

Abstract

The main factor effecting the thermal biology of eastern box turtles is the fact that these (and all) box turtles are ectotherms, meaning that they depend on external sources for heat and that their temperature is greatly affected by the ambient temperature. Box turtles are also considered poikilotherms, meaning that they experience a broad range of body temperatures that rise and fall with the environmental temperature (except at extreme temperatures, where they are able to employ physiological responses to maintain their body temperatures within a safe range) . The wide range of temperatures experienced by box turtles can significantly affect both physiological and behavioral processes.

As a result, we will measure the shell temperature of free-ranging eastern box turtles (Terrapene carolina) in Davidson, North Carolina, every fifteen minutes for a year using Thermocrom Ibuttons. This temperature data will be used to analyze the temperature variation in free-range box turtles. We will compare the average maximums and minimums to the average ambient maxiums and minimums, and compare average maximums and minimums between individual turtles. We will also examine the variation in average maxiumum and minimum shell temperatures throughout the year. Hopefully, these anaylses will give us a clearer picture of the types of temperature variation experienced by free - ranging box turtles throught the year.

Sample Data

Maximum and Minimum Shell Temperatures for an eastern box turtle, T. carolina, from May 26 through October 13th, 2004, in Davidson, NC. The red lines represent the maximum temperature at the box turtle's shell each day and the blue lines represent the minimum temperature at the box turtle's shell each day. The dip in the shell temperature on August 13-15 is most likely due to the large amounts of precipitation that occurred when Tropical Storm Bonnie passed through the area (J. Hester unpublished data).

A comparison of box turtle, air, and ground temperature for three days in May. The turtle's shell temperature is represented by the blue dotted line, the ground temperature by the yellow line, and the air temperature by the blue line. Notice that the turtle's temperature lags slightly behind the peaks in the air temperature and peaks about the same time as the ground temperature peaks. Also notice that the shell temperatures are never as high as the air temperature. (J. Hester unpublished data).