During terrestrial nesting forays, north-temperate freshwater turtles may experience a range of environmental temperatures that could cause overheating or constrain movement if temperatures are too high or low. Yet, we have very little understanding of how body temperature (Tb) varies in freshwater turtles during various nesting foray activities. We studied Tb variation in Chrysemys picta marginata from a small marsh in northern Michigan, 2003–2004. Three individuals left the marsh, nested, and returned to the marsh in a single day; whereas, 5 others remained on land for up to 3 days, mostly immobile under leaf litter. While on land, Tb of turtles and air temperature (Ta) showed parallel, diel oscillations. Mean Tb of mobile turtles exceeded prevailing Ta values but was similar to Tb recorded for those same individuals while aquatic 1 week before and after the nesting foray. Therefore, active nesting turtles on forays may have maintained suitable Tb values by use of sun or shade. During the nesting process, Tb decreased from 23.5°C to 20.0°C. Turtles that entered terrestrial refugia after evening nesting had Tb values similar to those while mobile, often at times when the evening sky illuminated the nesting areas. Therefore, low light levels, which could limit navigation, and Tb values, which could impede movements, did not directly cause turtles to seek terrestrial refugia after nesting. Instead, we suggest that impending low environmental temperatures, waning light levels that would eventually impair navigation abilities, and, ultimately, the risk of predation while returning to the marsh caused turtles to seek terrestrial refugia.
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Vol. 8 • No. 2