Short-duration flights are three times more costly than extended flight activity in an insectivorous bat

Flying animals face very high instantaneous costs of locomotion (flight metabolic rate ∼16 times basal metabolic rate in bats). However, the effect of flight duration is poorly studied. We hypothesized there is a metabolic transition from short burst to longer duration flights, and predicted a higher metabolic rate in short flights. We adapted the sodium bicarbonate isotopic tracer method to measure flight metabolic rate for durations up to 11 min in big brown bats (Eptesicus fuscus). We observed a ∼3-fold decrease in metabolic rate (V̇CO2) over the first ∼6 min of flight with predicted minimum V̇CO2=2.48±0.65 ml min-1. We discuss other aspects of the metabolic transition with flight duration as important avenues for further investigation. Implications include understanding evolutionary trade-offs among foraging strategies, revising energetic budget models and incorporating these aspects of the physiology of volant mammals into the mammalian exercise model.