We quantified oxygen consumption rates during overnight rest (RMR), and during forced exercise (MMR) using flow-through respirometry. The aerobic performance was measured from July until the end of August, which includes late-breeding, post-breeding and the initial autumn migration periods of great reed warblers . Because birds had just completed breeding or were in pre-migratory or migratory stages, the strict conditions of measuring BMR might not be fully met and, thus, we consider overnight oxygen consumption rates to represent RMRs .