Bird migration requires extraordinary physiological adaptations that transform these animals into the ultimate endurance athletes. Prior to migration, many species enter a state called hyperphagia—intense eating that can double their body weight through fat accumulation specifically designed for longdistance flight. Unlike mammals, birds can efficiently metabolize this fat directly through the bloodstream during flight. Bartailed godwits undertake the longest nonstop migration of any bird, flying 11,000 kilometers across the Pacific Ocean from Alaska to New Zealand without a single rest, remaining in continuous flight for nine days. To accomplish this feat, these birds temporarily shrink digestive organs they won't need during migration while simultaneously increasing heart and flight muscle size. Highaltitude migrants like barheaded geese, which cross the Himalayas at elevations exceeding 8,000 meters, have evolved hemoglobin with higher oxygen affinity and denser capillary networks in flight muscles. Perhaps most remarkably, many migratory species can put half their brain to sleep while keeping the other half awake during flight, an ability called unihemispheric slowwave sleep that enables rest without interrupting their journey. These specialized adaptations demonstrate how evolutionary pressures have crafted extraordinary biological solutions to the challenges of longdistance migration. Shutdown123