To effectively conserve migratory species, the entire range encompassed by their annual life cycle needs to be considered. Most research on Nearctic-Neotropical migratory birds has focused on the breeding grounds resulting in a general lack of knowledge regarding the wintering and migratory periods. The Canada Warbler (Cardellina canadensis) has declined by 71% from 1970 to 2012, at a rate of 2.9% per year, and is listed as Threatened in Canada. As with most Nearctic-Neotropical migrants, conservation efforts outside the breeding range are limited by a poor understanding of migration routes and the connectivity between specific breeding and wintering populations. To determine migratory routes of multiple breeding populations of Canada Warblers, we directly-tracked individuals using light-level geolocators deployed at four sites across the breeding range, spanning approximately 43 degrees in longitude (Alberta, Manitoba and Québec, Canada, and New Hampshire, USA). Twenty-five geolocators with usable data were recovered from three sites and were analyzed using FlightR to determine fall migration routes (n = 18) and individual wintering sites (n = 25). Individuals from all breeding populations took a western fall migration route at the Gulf of Mexico; with 77.8% of birds funnelling into a narrow geographic space along the western side of the Gulf of Mexico (97°W-99°W). We found no evidence for population-specific, parallel migration routes. Most individuals (72%) overwintered in Colombia. The remaining individuals overwintered in Venezuela. Our results demonstrate convergence of migratory routes around a migration barrier for individuals originating from widely distributed breeding areas. Further, we suggest the potential importance of habitat around the Gulf of Mexico during migration and Andean forest in Colombia as overwintering habitat for this threatened species. Future research should be directed at understanding how these areas are used by Canada Warblers.

中文翻译：

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加拿大莺（Cardellina canadensis）的广泛繁殖种群汇聚通过中美洲的迁移。

为了有效地保护迁徙物种，需要考虑其年度生命周期所涵盖的整个范围。对近北极—新热带候鸟的大多数研究都集中在繁殖地上，这导致人们普遍缺乏有关越冬和候鸟的知识。从1970年到2012年，加拿大莺（Cardellina canadensis）下降了71％，每年下降2.9％，在加拿大被列为“受威胁”。与大多数近北向新移民一样，由于对迁徙路线的了解不足以及特定繁殖与越冬种群之间的联系，限制了繁殖范围之外的保护工作。为了确定加拿大莺的多个繁殖种群的迁徙路线，我们使用分布在整个繁殖范围内四个地点（经度大约为43度）（加拿大艾伯塔省，曼尼托巴省和魁北克省以及美国新罕布什尔州）的轻型地理定位器直接跟踪了个体。从三个站点中检索了25个具有可用数据的地理定位器，并使用FlightR对其进行了分析，以确定秋季迁徙路线（n = 18）和各个越冬站点（n = 25）。来自所有繁殖种群的个体在墨西哥湾采取西部秋季迁徙路线。其中77.8％的鸟类沿墨西哥湾西侧（97°W-99°W）进入狭窄的地理区域。我们没有发现针对特定人群的平行移民路线的证据。大多数人（72％）在哥伦比亚过冬。其余的人在委内瑞拉过冬。我们的研究结果表明，对于来自广泛分布的繁殖地区的个体而言，围绕迁移障碍的迁移路线趋于一致。此外，我们建议在迁徙过程中墨西哥湾周围栖息地的潜在重要性和哥伦比亚的安第斯森林作为该受威胁物种的越冬栖息地的潜在重要性。未来的研究应该针对了解加拿大莺队如何使用这些区域。