Low metabolism in a tropical bat from lowland Panama measured using heart rate telemetry: an unexpected life in the slow lane

Animals must optimize their daily energy budgets, particularly if energy expenditures are as high as they are in flying animals. However, energy budgets of free-ranging tropical animals are poorly known. Newly miniaturized heart rate transmitters enabled this to be addressed this in the small, energetically limited, neotropical bat Molossus molossus. High-resolution 48 h energy budgets showed that this species significantly lowers its metabolism on a daily basis, even though ambient temperatures remain high. Mean roosting heart rate was 144 beats min(-1), much lower than expected for a 10 g bat. Low roosting heart rates combined with short nightly foraging times (37 min night(-1)) resulted in an estimated energy consumption of 4.08 kJ day(-1), less than one-quarter of the predicted field metabolic rate. Our results indicate that future research may reveal this as a more common pattern than currently assumed in tropical animals, which may have implications in the context of the effect of even small temperature changes on tropical species.