Thermal Aspects of Nesting Ecology of the Texas River Cooter (Pseudemys texana) and Red-Eared Slider (Trachemys scripta elegans) at Spring Lake, Hays County, Texas
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Texas river cooters (Pseudemys texana) and red-eared sliders (Trachemys scripta elegans) are large-bodied freshwater emydid turtles common in Central Texas. Previous studies have focused on diet, growth, body size, and reproductive potential, but there is little published information on adult female thermal relationships and nesting ecology. Thermal ecology is important to turtles not only for their metabolism and growth (Thornhill, 1982) but it can be fatal if they are exposed to high temperatures (Hutchison et al., 1966). I recorded weather parameters, water temperatures, ground surface temperatures, and internal and external body temperatures of emerging Texas river cooters (n=52) and red-eared sliders (n=18). Temperatures were also recorded for 48 Texas river cooters and 16 red-eared sliders upon completion of nesting. I also examined whether an association exists between cloacal temperatures of Texas river cooters with algae and mud carapaces that might serve as a thermal buffer while they are in the process of nesting. Of those I recorded completing nests, 68.9% of Texas river cooters and 56.3% of red-eared sliders did so in May. Texas river cooters (78%) and red-eared sliders (73.3%) emerged at water temperatures between 22°C and 26°C. Texas river cooters (85%) and red-eared sliders (89%) also emerged when ground surface temperatures were between 20°C and 35°C. The majority of Texas river cooters (68.9%) and red-eared sliders (56.3%) completed nests in May. Red-eared sliders seem to incur higher internal temperatures at nest completion than Texas river cooters. There is a strong positive correlation between the cloacal temperatures at nest completion of Texas river cooters (r = 0.7750274, P < 0.001,) and red-ear sliders (r = 0.751557, P < 0.001) to ground surface temperatures. More red-eared sliders (43.8%) seem to complete nests in warmer portions of the day when the ground temperatures are between 30°C and 35°C, while Texas river cooters (37.5%) complete nests when ground temperatures are between 25°C and 30°C. This information provides valuable insight into the nesting ecology of these turtles that has not previously been documented.