Depleted lean body mass after crossing an ecological barrier differentially affects stopover duration and refueling rate among species of long-distance migratory birds

During the long-distance migratory flights of birds, lean mass breakdown occurs in concert with fat catabolism and is expected to have repercussions on total stopover duration because birds require time to rebuild lean tissue before accumulating fat reserves. Despite this, little is known about the role of in-flight lean mass breakdown on stopover duration because direct measurements are restricted by the destructive nature of traditional body composition analysis and the technological limitations of tracking small birds over large expanses. We used non-lethal, non-invasive Quantitative Magnetic Resonance technology and plasma metabolite profiling to measure the body composition and physiological state of free-living birds captured at a migratory stopover site after flight across the Gulf of Mexico, and an automated radiotelemetry array covering ~5000 km2 to track stopover duration and regional movements. We tested whether stopover duration is prolonged in individuals arriving with lowe...