Metabolic rate of 12 Pipistrellus nathusii in relation to varying airspeed. We measured the metabolic rate of flying bats in a wind tunnel using the 13C labeled Na-bicarbonate method. The relationship between metabolic rate and airspeed was U-shaped in the majority of individuals. We could not find a U-shaped curve in a few individuals that engaged in flight manoeuvers, including landing. We used the shape of the U-shaped power curve to estimate minimum flight speed and maximum range speed for the study species. Further we present data on migration speed (n=37) and foraging flight speed (n=40) in wild Pipistrellus nathusii at a major miratory corridor in Latvia.