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，源自器官与肌肉的蛋白质分解代谢（protein catabolism）对于合成葡萄糖、关键代谢中间产物及水分而言不可或缺，但该过程可能对飞行距离以及中途停歇地（stopover）的能量补给产生不利影响。我们对既往研究提出的假说进行了验证：取食高蛋白昆虫日粮的鸟类，在飞行过程中用于供能的蛋白质占比高于取食高碳水水果日粮的鸟类。首先，我们为迁徙性黄腰林莺（yellow-rumped warbler）饲喂合成水果日粮或混合昆虫/水果日粮，并在基础静息状态以及跳跃/悬停轮式呼吸测定仪（hop/hover wheel respirometer）检测的运动状态下，测定了其代谢率（metabolic rates）与供能底物配比（fuel mixture）。取食水果日粮的个体血浆甘油三酯（plasma triglyceride）与非酯化脂肪酸（non-esterified fatty acid）浓度更高，而高蛋白混合日粮仅在饲喂阶段提升了血浆尿酸（plasma uric acid）浓度。日粮组成对静息或运动状态下的代谢率及供能底物配比均无显著影响。随后，我们为黄腰林莺饲喂仅碳水化合物与蛋白质相对比例存在差异的合成日粮（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（wind tunnel flights）实验中对其进行测试。饲喂高碳水日粮的鸟类体重与体脂含量均高于饲喂高蛋白日粮的个体。在飞行前状态（经过3小时禁食后），高蛋白日粮提升了血浆尿酸浓度并降低了血浆磷脂（plasma phospholipid）浓度；但仅在飞行过程中，日粮组成才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。日粮组成与体脂储备量均未对飞行过程中的瘦体重（lean mass）或脂肪丢失速率产生影响。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，饲喂高碳水日粮的鸟类自主飞行时长（voluntary flight duration）更长，且该差异与体脂含量无关，这表明高碳水日粮对迁徙鸟类可能存在其他性能收益。