Data from: Linking the wintering and breeding grounds of warblers along the Pacific Flyway

Long-distance migration is a behavior that is exhibited by many animal groups. The evolution of novel migration routes can play an important role in range expansions, ecological interactions, and speciation. New migration routes may evolve in response to selection in favor of reducing distance between breeding and wintering areas, or avoiding navigational barriers. Many migratory changes are likely to evolve gradually and are therefore difficult to study. Here, we attempt to connect breeding and wintering populations of myrtle warblers (Setophaga coronata coronata) to better understand the possible evolution of distinct migration routes within this species. Myrtle warblers, unlike most other warblers with breeding ranges primarily in eastern North America, have two disjunct overwintering concentrations—one in the southeastern USA and one along the Pacific Coast—and presumably distinct routes to-and-from these locations. We studied both myrtle and Audubon's warblers (S. c. auduboni) captured during their spring migration along the Pacific Coast, south of the narrow region where these two taxa hybridize. Using stable hydrogen isotopes and biometric data, we show that those myrtle warblers wintering along the southern Pacific Coast of North America are likely to breed at high latitudes in Alaska and the Yukon rather than in Alberta or further east. Our interpretation is that the evolution of this wintering range and migration route along the Pacific Coast may have facilitated the breeding expansion of myrtle warblers into northwestern North America. Moreover, these data suggest that there may be a migratory divide within genetically similar populations of myrtle warblers.

长距离迁徙是众多动物类群所展现的典型行为。全新迁徙路线的演化，在物种分布范围扩张、生态相互作用以及物种形成过程中均可发挥关键作用。新迁徙路线的演化往往是为了响应选择压力，以缩短繁殖地与越冬地之间的距离，或是规避导航障碍。多数迁徙相关的演化改变均以渐进方式发生，因此相关研究颇具难度。本研究旨在关联黄腰林莺（Setophaga coronata coronata）的繁殖种群与越冬种群，以深入解析该物种内部不同迁徙路线的潜在演化机制。与多数繁殖范围主要位于北美东部的其他林莺物种不同，黄腰林莺存在两处相互隔离的越冬聚集区：一处位于美国东南部，另一处则沿北美太平洋海岸分布，且往返这两处越冬地的迁徙路线大概率存在显著差异。我们对春季迁徙期间在太平洋海岸沿线（两类群杂交狭窄区域以南）捕获的黄腰林莺与奥杜邦林莺（S. c. auduboni）进行了采样研究。本研究通过稳定氢同位素与生物测量数据，证实沿北美太平洋海岸南部越冬的黄腰林莺，其繁殖地大概率位于阿拉斯加与育空的高纬度区域，而非阿尔伯塔或更靠东的地区。据此我们推测，沿太平洋海岸分布的越冬范围与迁徙路线的演化，可能推动了黄腰林莺的繁殖范围向北美西北部扩张。此外，本研究数据还表明，在遗传相似度较高的黄腰林莺种群内部，或许存在迁徙路线分化现象。