Behavioral plasticity can buffer animals against physiological impacts of climate change, but research is needed to understand the limits and consequences of behavioral responses to warming. Increased night activity by diurnal animals is a potential response to warming thought to require considerable behavioral flexibility. We hypothesized that juvenile Mojave desert tortoises (Gopherus agassizii), diurnal ectotherms that typically rely on burrows to conserve limited energy and water reserves during summer, may respond to rising burrow temperatures by shifting from using burrows at night to overnighting at the surface where cooler temperatures reduce metabolic expenditure. This strategy could be energetically adaptive but may increase predation risk. Using time-lapse cameras at burrows and iButton temperature loggers affixed to juveniles and placed at burrow and surface microhabitats during a summer heatwave, we found that individuals often emerge from burrows on evenings when their temperatures approach the voluntary thermal maximum of well-fed, hydrated laboratory animals. Tortoises remained inactive at the surface before returning to burrows after sunrise. By shifting to surface microhabitats at night, tortoises dramatically reduced nighttime body temperatures and energy expenditure during the heatwave. Future research will examine whether this behavioral adjustment to temperature entails greater predation risk.