The effects of dietary macronutrients on flight ability, energetics, and fuel metabolism of yellow-rumped warblers Setophaga coronata

The catabolism of protein from organs and muscles during migratory flight is necessary to produce glucose, key metabolic intermediates, and water, but may have negative effects on flight range and refueling at stopovers. We tested the hypothesis, suggested by previous studies, that birds that eat high-protein insect diets use more protein for fuel in flight than those that eat high-carbohydrate fruits. First, we fed migratory yellow-rumped warblers synthetic fruit or mixed insect/fruit diets, and measured metabolic rates and fuel mixture under basal conditions and during exercise in a hop/hover wheel respirometer. Birds eating the fruit diet had greater plasma triglyceride and non-esterified fatty acid concentrations, and the higher protein mixed diet increased plasma uric acid only during feeding. Diet did not affect metabolic rates or the fuel mixture under resting or exercise conditions. We then fed yellow-rumped warblers synthetic diets that differed only in the relative proportion ...