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是生成葡萄糖、关键代谢中间产物及水分的必要途径，但可能对飞行距离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：取食高蛋白昆虫类食物的鸟类，在飞行中用于供能的蛋白质比例高于取食高碳水化合物果实类食物的鸟类。首先，我们为迁徙性黄腰林莺喂食合成果实饲料或昆虫-果实混合饲料，并在基础代谢状态及跳跃悬停轮式呼吸测定仪的运动测试状态下，测量其代谢率与供能底物组成。取食果实饲料的个体血浆甘油三酯与非酯化脂肪酸浓度更高；而高蛋白混合饲料仅在喂食期间提升了血浆尿酸浓度。无论处于静息还是运动状态，饲料类型均未影响代谢率或供能底物组成。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合成饲料（干物质占比分别为60:15与15:60），并在持续时长可达6小时的风洞飞行试验中对其开展测试。喂食高碳水化合物饲料的个体，体重与体脂量均高于喂食高蛋白饲料的个体。飞行前状态（经3小时禁食后）下，高蛋白饲料提升了血浆尿酸浓度，却降低了血浆磷脂浓度；而在飞行过程中，饲料仅对血浆磷脂浓度产生影响（高蛋白组个体的血浆磷脂浓度更低）。无论是饲料类型还是体脂储备量，均未对飞行过程中的瘦体重或脂肪消耗速率产生影响。个体间或季节间的饮食差异，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，喂食高碳水化合物饲料的个体自主飞行时长更长，且这一差异与体脂量无关，这提示高碳水化合物饲料可能为迁徙鸟类带来其他飞行性能方面的益处。