Warm nocturnal temperatures act as an ecological trap for a diurnal lizard

The effects of increasing nighttime temperatures remain underexplored, despite that nocturnal temperatures are rising at a faster rate than diurnal temperatures and are expected to negatively impact fitness‐relevant physiological processes such as clearing of metabolic wastes, repairing cellular damage, and growth. An initial response to warming environments is behavioral thermoregulation, which enables ectotherms to rapidly adjust to changing conditions. The behavioral responses of ectotherms to warmer diurnal temperature have been well‐documented; however, little is known about nocturnal thermoregulation. In this study, we experimentally assessed the impact of elevated nocturnal temperatures on retreat site selection and thermoregulation strategies in the diurnal common wall lizard Podarcis muralis . Using semi‐natural mesocosms, we exposed adult male lizards to two distinct nocturnal temperature treatments (control versus a ~ 4°C increase) and recorded their body temperatures continuously over two weeks with wearable temperature loggers. Lizards in the warmer treatment selected warmer nocturnal retreats and exhibited significant among‐individual variation in nocturnal site choice. Furthermore, there was no shift in selected diurnal temperatures to compensate for nocturnal exposure. Lizards in the warm treatment suffered greater reduction in body condition by the end of the experiment, suggesting that the behavioral response to warmer nocturnal temperatures does not mitigate the physiological costs. This study confirms the potential for nocturnal warming to create an ecological trap for diurnal species: lizards will select warmer temperatures when available at night, despite these behaviors being potentially maladaptive. Our findings underscore the need for further research on the long‐term impacts of nocturnal warming on fitness and the adaptive limits of plastic responses in diurnal ectotherms.