STONE, M.D.**; HELLGREN, E.C.; Oklahoma State University; Southern Illinois University: Thermal Variation in the Microhabitat of the Texas Tortoise (Gopherus berlandieri)

Texas tortoises potentially experience harsh thermal regimes during summer months. It is therefore likely that environmental temperature significantly influences activity patterns. Although thermoregulatory and heat exchange studies have been conducted on Gopherus berlandieri, few data exist concerning the thermal properties of their microhabitat. Moreover, development of miniature data loggers has facilitated the continuous tracking of temperature data in the field and reduced variance associated with one-point measurements. We continuously monitored the thermal properties of G. berlandieri microhabitat by affixing ibutton® (Dallas/Maxim Semiconductors) temperature data loggers to the carapace of 6 and 14 tortoises during the summer of 2005 and 2006, respectively. In 2005 temperature values were collected every 5 minutes for at least 60 days between May 25th and August 10th. In 2006 we monitored every 8 minutes between June 7th and August 9th. We also monitored ambient temperatures in the shade and sun from a Stevenson Screen. Preliminary data suggest that tortoises experience temperatures that are lower than ambient during daylight hours; however, tortoises generally experience temperatures higher than ambient between dusk and dawn. This suggests that Gopherus berlandieri may buffer temperature exposure by selecting microhabitat that reduces variation in temperature.