Behavioral and Physiological Responses to Simulated Predator Induced Stress in the Eastern Box Turtle, Terrapene carolina carolina

Abstract

The behavioral and physiological responses of eastern box turtles, Terrapene carolina carolina, to a simulated predatory encounter were measured. Wild box turtles were randomly assigned to a stimulus intensity group, which consisted of observation (control), a visual stimulus, a poke on the leg, or a pinch on the leg before being flipped. Behavior in response to the stimulus was observed from a distance for 5 minutes, except for the control which was observed for 15 minutes. Immediately after the observation period, turtles were captured and had a small blood sample taken, after which a pinch gauge was used to measure the shell’s closing force. The results indicate that the stronger the simulated predatory stimulus, the stronger the behavioral responses, with the turtles taking more advantage of their fully closable shell at the more intense stimulus groups. However, stimulus intensity did not affect the plasma corticosterone or plasma lactate response. This may be due to too short or weak of a stimulus, increased parasympathetic activity, or seasonal effects. Upon capture and during handling almost all turtles withdrew into their shells and closed their anterior plastron, although fewer actually closed their posterior plastron, and a few engaged in other behaviors such as biting, urinating, and air walking. There appeared to be a correlation between box turtle size and pinch strength; however, the relatively large size of the pinch gauge may have put smaller turtles at a disadvantage compared to larger turtles because of excessive stretching of their closing muscles. The results of this study indicate that in spite of their fully closable shell, box turtles exhibit a complex, graded response to perceived threats. This strongly suggests that full closure of the shell is likely to be costly and occurs only in response to the most intense stimuli.