Basal metabolic rate declines during long-distance migratory flight in great knots

Great Knots (Calidris tenuirostris) make one of the longest migratory fligh ts in the avian world, flying almost 5500 km from Australia to China during northward migration. We measured basal metabolic rate (BMR) and body compo sition in birds before and after this flight and found that BMR decreased 4 2%. The mass-specific BMR based on lean mass decreased 33%. We also starved a group of pre-migratory Great Knots in captivity to determine whether the y showed the same reduction in BMR without having undergone the hard work o f flight. The captive birds showed a similar range and reduction of BMR val ues as the wild birds. Exponents of relationships between BMR and body mass in different comparisons were high, indicating large changes in BMR as a f unction of body mass. Analysis of the body composition of ten wild and thre e captive birds found that the flight muscle mass and intestine mass positi vely correlated with BMR.