Behavioral and Physiological Differences in Migratory Strageties of a Long-distance Migrant, the Blackpoll Warbler, and a Facultative Short-distance Migrant, the Yellow-rumped Warb

候鸟在迁徙途中会选择何时何地休息并补充能量储备，通常是在它们从未去过的地方，而且食物和天气可能无法预测的时候。 它们能否以良好的状态及时到达目的地，会影响它们获得最佳越冬或繁殖地的机会，从而影响它们的生存或繁殖成功。 黑鸟莺，Dendroica straiata，几乎是它的体重与脂肪储备的两倍，因为它准备跨大西洋迁移到南美洲过冬。 这一物种在迁徙过程中的体重损失率最低。 这表明它们能更有效地利用脂肪，并且能比许多其他鸟类更长时间地利用骨骼肌作为能量储备。 相比之下，虽然黄腰莺，Dendroica coronata，在繁殖地与Blackpoll莺重叠，但它是一种短距离迁徙（主要是陆地），并没有如此广泛的脂肪储备。 本研究的重点是探讨这两种莺在行为和生理上的差异，反映了它们不同的迁徙能量需求。 在这个项目中，主要重点是皮质酮和相关代谢物在控制食物摄入和脂肪储备中的作用。 一系列的实验室和实地研究将调查可能的差异，在这两个物种的皮质酮分泌的模式，可能反映他们的不同模式的育肥和他们各自的需要，以保护骨骼肌在迁移过程中。 在实验室研究中，研究员将调查皮质酮在调节鸟类能量需求的季节性变化方面是否有多种作用，以及这两个物种对皮质酮对肥育和肌肉蛋白质利用的影响是否有不同的阈值。 通过了解具有不同能量需求的鸟类如何进化以满足最佳条件下的迁徙挑战。我们将更了解当天气和栖息地质素等情况恶化时，鸟类的行为和生理限制。 该项目的结果可以说明在迁徙期间遇到的环境因素如何影响整个年度周期的鸟类种群。

Migrating birds make choices en route about where and when to rest and replenish energy reserves, often in areas they have never visited before and at a time when food and weather may be unpredictable. Their ability to reach their destinations in good condition and in a timely manner can influence their chances of gettting the best wintering or breeding territories and, thus, influence their survivorship or reproductive sucess. The Blackpoll Warbler, Dendroica straiata, almost doubles its body mass with fat reserves as it prepares for a trans-oceanic migration over the North Atlantic to winter in South America. This species has been found to have the lowest rate of weight loss during migration. This suggest that they use fat more efficiently and can spare skeletal muscle for use as energy reserves longer than many other birds. In contrast, while the Yellow-rumped warbler, Dendroica coronata, overlaps with the Blackpoll warbler on its breeding grounds, it is a short-distance migrant (primarily overland) and does not put on such extensive fat reserves. The focus of this study is to investigate differences in the behavior and phsiology of these two species of warblers that reflect their different energetic demands of migration. In this project, the primary emphasis is on the role of corticosterone and related metabolites in controlling food intake and fat reserves. A series of laboratory and field studies will investigate possible differences in patterns of corticosterone secreation in these two species that may reflect their different patterns of fattening and their respective need to protect skeletal muscle during migration. In laboratory studies, the PIs will investigate the possibility that corticosterone has multiple roles in regulating the seasonal changes in energy demand in birds and that these two species may have different threshold for corticosterone's effects on fattening and muscle protein utilization. By understanding how birds with different energetic demands have evolved to meet the challenges of migration under optimal conditions. we will have a greater understanding of the behavioral and physiological constraints of birds when conditions such as weather and habitat quality deteriorate. The results from this project may illustrate how environmental factors encountered during the migratory period may impact bird populations throughout the annual cycle.