Effects of Slope, Substrate, and Temperature on the Locomotion of the Ornate Box Turtle, Terrapene ornata

Ornate box turtles, from the Sand Hills of Nebraska, live in a habitat characterized by slopes, a fine sand substrate, and temperatures that can vary greatly, both diurnally and seasonally. We examined the locomotor responses of these turtles to slope, substrate, and temperature. Only 25% of the turtles could successfully walk on slopes as steep as −40°. They were better at walking upslope, but their speed progressively decreased as slope increased. As grade increased, they primarily adjusted stride frequency on upslopes but stride length on downslopes. Turtles appear to be much more affected by slopes than are lizards. Speed was significantly reduced on sand substrates in comparison to Styrofoam, and this was primarily because of a reduction in effective stride length. Speed increased with increasing temperature from 20 to 35 C, almost entirely resulting from an increase in stride frequency; however, the Q₁₀ for locomotor performance was low. Turtle speeds in the field averaged 0.05 m/s, and, although there was a tendency for higher speeds at higher operative environmental temperatures, this was not statistically significant. Within their natural Sand Hill habitat, these turtles are often active under conditions of slope, substrate, and temperature that are suboptimal for locomotion. However, locomotor performance is not adversely affected to any appreciable degree by the potential constraints of their habitat.

Fig. 1.

The effects of slope on mean speed (A), stride length (B), and stride frequency (C) of ornate box turtles. Open circles depict the means and vertical lines one standard error above and below the mean. Sample size was five for the −40° slope and 19 for all other slopes. Within each graph, for slopes of −20° and above, symbols with a lower case letter in common do not differ significantly (P > 0.05)

Fig. 2.

A comparison of the relative effects of slope on stride length and stride frequency of ornate box turtles. All values are expressed as a percentage of the values on a horizontal surface

Fig. 3.

The relationship between body mass and the speed of 19 ornate box turtles on horizontal surfaces and upslopes. The correlation for 0 degrees is statistically significant (P < 0.01)

Fig. 4.

The effects of substrate on speed (A), stride length (B), and stride frequency (C) of ornate box turtles. Sample size was 21. See Figure 1 for further explanation of symbols

Fig. 5.

The relationship between body mass and the speed of ornate box turtles on three different substrates. The correlation for the fine sand data is statistically significant (P < 0.01)

Fig. 6.

The effects of temperature on speed (A), stride length (B), and stride frequency (C) of ornate box turtles. Sample size was 22. See Figure 1 for further explanation of symbols

Fig. 7.

The effects of slope on the speed (relative to horizontal) of three species of turtles and 16 species of lizards. Sources of data: Terrapene ornata, present study; Terrapene carolina, Muegel and Claussen, 1994; Chelydra serpentina, Finkler and Claussen, 1997; Callisaurus draconoides, Irschick and Jayne, 1998; Uma scoparia, Jayne and Ellis, 1998; Stellio stellio, Huey and Hertz, 1982. Lacertid lizards (the symbols represent the values for 13 different species), Vanhooydonck and Van Damme, 2001. Except for S. stellio, all lizards depicted were tested on only one upslope