Migratory flight is energetically challenging, requiring alternating phases of fuel catabolism and fuel accumulation, accompanied by dramatic changes in body composition and behavior. Baseline corticosterone (CORT; the primary glucocorticoid in birds) is thought to underlie transitions between fuel catabolism during flight, fuel deposition during stopover, and the initiation of migratory flight. However, studies of CORT on stopover physiology and behavior remain disparate efforts, lacking the cohesion of a general hypothesis. Here we develop a Stopover-CORT hypothesis formalizing the relationships among CORT, body condition, and refueling rate in migratory birds. First we expect body mass to increase with triglycerides (TRIG) as birds refuel. Second, based on a synthesis of previous literature, we predict a U-shaped CORT curve over the course of stopover, postulating that elevated CORT at arrival is reactive, responding to poor body condition, while CORT elevation before departure is preparative, driving changes in behavior and body condition. We tested these predictions in Gray Catbirds (Dumetella carolinensis) following a trans-Gulf flight during spring migration. We found baseline CORT was negatively correlated with body condition and TRIG, corresponding with our predictions for arriving and refueling-but not departing-birds. It is possible catbirds undergo regional habitat translocations rather than complete the entire stopover phase at our study site. We propose the Stopover-CORT hypothesis as a useful predictive framework for future studies of the mechanistic basis of stopover physiology. By studying the regulation of stopover refueling and departure, we may better understand physiological limitations to overall migration rate and improve assessments of habitat quality for refueling birds.

中文翻译：

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建立中途停留-CORT假设：皮质酮预测候鸟中途停留期间灰Gray的身体成分和加油率。

迁徙飞行是一项充满挑战的挑战，需要交替进行燃料分解代谢和燃料积累，并伴随着身体成分和行为的急剧变化。基线皮质酮（CORT；鸟类中的主要糖皮质激素）被认为是飞行过程中燃料分解代谢，中途停留过程中燃料沉积和迁徙飞行开始之间的过渡的基础。然而，关于中途停留生理和行为的CORT研究仍然是不同的努力，缺乏一般假设的凝聚力。在这里，我们建立了一个Stopover-CORT假设，正式确定了候鸟中CORT，身体状况和加油率之间的关系。首先，我们期望随着鸟类加油，甘油三酸酯（TRIG）会使体重增加。其次，根据以往文献的综合，我们预测了中途停留期间的U形CORT曲线，假定到达目的地的CORT升高是反应性的，对身体状况不佳做出反应，而出发前的CORT升高是预备的，从而驱动了行为和身体状况的变化。我们在春季迁徙过程中进行跨海湾飞行后，在灰猫（Dumetella carolinensis）中测试了这些预测。我们发现基线CORT与身体状况和TRIG负相关，与我们对到达和加油的预测（而不是离场的鸟类）的预测相对应。cat鸟可能会经历区域栖息地移位，而不是在我们的研究地点完成整个中途停留阶段。我们提出了Stopover-CORT假设，作为将来对中途停留生理学的机械基础进行研究的有用的预测框架。