Torpor is a widely used energy saving strategy in small heterothermic mammals. Measuring body temperature is a common method used to infer energy consumption and torpor use. However, it has recently been shown that heart rate is a more accurate predictor of metabolic rate than body temperature in two tropical bat species. To put these findings into a broader context, we simultaneously measured continuous heart rate, body temperature and metabolic rate in females from a temperate zone bat species (Nyctalus noctula). We investigated energy saving strategies across three reproductive stages at seasonal and varied ambient temperatures. We found that pregnant bats lowered their body temperature to adapt to ambient temperatures less often than non-reproductive bats. Instead they were able to independently lower their heart rate to save energy. We confirm that heart rate better predicts metabolic rate than the traditionally used body temperature and show that across all reproductive stages, bats can express very low heart rates at high body temperatures. With these novel findings in a temperate bat species, bats from at least three different families can flexibly adapt their physiological state to current life history stage and ambient conditions, saving energy through adjusting heart rates independently of body temperature. This emphasizes the need to revise the definition of torpor as an energy saving strategy.