Endocrine and behavioral response to a decline in habitat quality: effects of pond drying on the slider turtle, Trachemys scripta.

The effect of the simulated drying of a pond on the behavior and corticosterone secretion of Trachemys scripta was measured in a field situation. Slider turtles were held in experimental and control ponds (12 x 15 m) enclosed with a drift fence integrated with spring-triggered livetraps. The experimental pond water level was dropped 10 cm per day for 8 d, until water was completely drained. Slider turtles responded to the draining of the pond by the emigration of the majority (75%) of the experimental population. Emigrating turtles had significantly elevated corticosterone at Time 0 (blood sample within 10 min of handling=4.48 ng/mL+/-0.503SE) when compared with turtles captured in a control pond (Time 0=0.954 ng/mL+/-0.121SE), where conditions were held constant. Turtles emigrated during the final 72 hr of pond draining when ponds reached 30 cm depth and lower and water temperature was at least 30.8 degrees C or higher. Additionally, the effect of trapping using spring-activated livetraps was tested. Turtles held in livetraps (n=6) for 45-110 min showed a characteristic corticosterone response (Time 0=0.957 ng/mL+/-0.091SE; Time 30=2.85 ng/mL+/-0.131SE), indicating that this trapping technique alone does not stimulate corticosterone secretion. The findings of the study met our predictions that turtles would respond to the draining of the pond behaviorally by emigrating from the habitat concurrent with an elevated corticosterone concentration. This supports the view that corticosterone is involved in stress avoidance mechanisms that allow organisms to respond to environmental perturbations.