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，机体器官与肌肉的蛋白质分解代谢对于生成葡萄糖、关键代谢中间产物及水分而言必不可少，但可能对飞行范围以及中途停歇地的能量补给产生负面影响。我们验证了此前研究提出的假说：取食高蛋白昆虫日粮的鸟类，在飞行过程中消耗的蛋白质燃料比例，高于取食高碳水化合物水果日粮的鸟类。首先，我们为迁徙黄腰林莺喂食人工合成的水果日粮或混合昆虫/水果日粮，并在基础代谢状态与跳跃/悬停轮式呼吸仪的运动状态下，测定其代谢率与代谢燃料组成。取食水果日粮的个体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进食阶段可升高血浆尿酸浓度。无论静息状态还是运动状态，日粮类型均未对代谢率或代谢燃料组成产生影响。随后，我们为黄腰林莺喂食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（干重占比分别为60:15与15:60），并在持续时长可达6小时的风洞飞行实验中开展测试。取食高碳水日粮的个体体重与体脂量均高于取食高蛋白日粮的个体。在飞行前状态（经3小时禁食后），高蛋白日粮会升高血浆尿酸浓度并降低血浆磷脂浓度；但仅在飞行过程中，日粮才会对血浆磷脂浓度产生影响——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或脂肪的流失速率产生影响。个体间或季节间的日粮差异似乎并不会改变耐力飞行期间的蛋白质分解代谢水平。然而，取食高碳水日粮的个体自主飞行时长更长，且该差异与体脂量无关，这表明高碳水日粮或许能为迁徙鸟类带来其他性能层面的益处。