Data from: 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 of carbohydrate and protein (60:15 versus 15:60 as % dry mass) and tested them in wind tunnel flights lasting up to six hours. Birds fed the high carbohydrate diet became heavier and fatter than when fed the high protein diet. Plasma uric acid concentration was increased and plasma phospholipid concentration was decreased by the high protein diet in the pre-flight state (after a 3 h fast), but diet only affected plasma phospholipids during flight (lower in high protein birds). Neither diet nor amount of body fat affected the rate of loss of lean mass or fat during flight. Inter-individual or seasonal differences in diet do not appear to influence the amount of protein catabolized during endurance flight. However, birds fed the high carbohydrate diet had greater voluntary flight duration, independent of body fatness, suggesting that there may be other performance benefits of high carbohydrate diets for migratory birds.迁徙飞行过程中，器官与肌肉的蛋白质分解代谢（protein catabolism）对于生成葡萄糖、关键代谢中间产物及水分而言是必需的，但该过程可能对飞行航程以及迁徙中途停歇地（stopover）的能量补给产生负面影响。我们验证了此前多项研究提出的假说：取食高蛋白昆虫日粮的鸟类，在飞行过程中会比取食高碳水化合物果实日粮的鸟类消耗更多蛋白质作为代谢燃料。首先，我们为迁徙中的黄腰林莺（yellow-rumped warbler）投喂人工合成的果实日粮或昆虫-果实混合日粮，并分别在基础代谢状态与跳跃悬停轮式呼吸仪（hop/hover wheel respirometer）中的运动状态下，测量其代谢率与代谢燃料组成。结果显示，取食果实日粮的个体，其血浆甘油三酯与非酯化脂肪酸浓度更高；而高蛋白混合日粮仅在投喂期间会升高血浆尿酸浓度。日粮类型对静息或运动状态下的代谢率及代谢燃料组成均无显著影响。随后，我们为黄腰林莺投喂仅碳水化合物与蛋白质相对比例存在差异的人工合成日粮（干物质占比分别为60:15与15:60），并在持续时长可达6小时的风洞飞行实验中对其进行测试。结果表明，取食高碳水化合物日粮的鸟类，其体重与体脂含量均高于取食高蛋白日粮的个体。飞行前状态（经过3小时禁食后）下，高蛋白日粮会升高血浆尿酸浓度并降低血浆磷脂浓度；而在飞行过程中，日粮仅会影响血浆磷脂浓度——高蛋白日粮组鸟类的血浆磷脂浓度更低。无论是日粮类型还是体脂储备量，均未对飞行过程中瘦体重（lean mass）与脂肪的损耗速率产生影响。个体间或季节性的日粮差异，似乎并不会影响耐力飞行过程中的蛋白质分解代谢量。然而，取食高碳水化合物日粮的鸟类，其自主飞行时长更长，且该差异与体脂含量无关，这表明高碳水化合物日粮可能为迁徙鸟类带来其他方面的飞行性能益处。