Data from: Differential migratory timing of western populations of Wilson’s Warblers revealed by mitochondrial DNA and stable isotopes

Molecular markers and stable isotopes have provided important insights into the migratory connectivity of small landbirds. Research integrating these two methods has primarily focused on linking breeding and wintering sites, rather than focusing on timing of migratory movement of different breeding populations. We used mitochondrial DNA and isotopic markers to infer the timing of various breeding populations of migrating Wilson's Warblers (Cardellina pusilla) moving through a migratory stopover site, demonstrating the value of multiple sources of information in estimating the origin of migrants. Using mixed-stock analysis, we found that early spring migrants sampled in southwestern Arizona were dominated by warblers migrating to the West Coast of the contiguous United States, whereas later migrants included a large pulse of birds migrating to Alaska and western Canadian provinces. Stable hydrogen isotope data from individual birds showed the same timing pattern as genetic data. Had we used stable isotopes alone, we would not have been able to infer whether birds later in the migration season were most likely migrating to Alaska or the Interior West, given the large overlap in isotope values between those regions. The lack of mitochondrial group 2, common in the Interior West, in late-season migrants strongly suggests that these birds were migrating to breeding areas in Alaska or other northern regions. Studies that reveal the timing of migration of different breeding populations through stopover sites lay the foundation for more in-depth examination of seasonal interactions between migration and the stationary phases of the annual cycle.

分子标记（molecular markers）与稳定同位素（stable isotopes）为小型陆鸟的迁徙连通性（migratory connectivity）研究提供了重要视角。整合这两类方法的相关研究，主要聚焦于繁殖地与越冬地的关联，而非不同繁殖种群的迁徙活动时序。本研究借助线粒体DNA（mitochondrial DNA）与同位素标记（isotopic markers），对途经某迁徙停歇地（migratory stopover site）的威氏莺（Wilson's Warbler, *Cardellina pusilla*）不同繁殖种群的迁徙时序进行推断，证实了多源信息在估算迁徙个体起源地方面的应用价值。通过混合种群分析（mixed-stock analysis），我们发现：在亚利桑那州西南部采样的春季早期迁徙个体，主要为前往美国本土西海岸的威氏莺；而后期迁徙个体中，则包含大量前往阿拉斯加及加拿大西部省份的种群。个体鸟类的稳定氢同位素（stable hydrogen isotope）数据，与遗传数据呈现出一致的时序模式。若仅依赖稳定同位素数据，鉴于阿拉斯加与内陆西部（Interior West）区域的同位素值存在显著重叠，我们将无法推断迁徙季后期的个体最有可能前往阿拉斯加还是内陆西部的繁殖地。迁徙季后期的个体中未出现内陆西部区域常见的线粒体类群2（mitochondrial group 2），这强烈表明此类个体的繁殖地位于阿拉斯加或其他北部区域。阐明不同繁殖种群途经停歇地的迁徙时序的相关研究，可为更深入探究迁徙与年度周期内停留阶段间的季节关联奠定基础。