Migratory bottlenecks concentrate individuals and populations of Nearctic–Neotropical migrants from across vast breeding areas. The extent to which such concentrations occur has important ramifications for interpreting migratory connectivity and for the vulnerability of populations throughout the annual cycle but investigations of such phenomena are rare. We inferred breeding origins of 11 species of Nearctic–Neotropical migrants captured during fall migration in the Darién region, northwestern Colombia, using feather stable-hydrogen isotope values (δ ²H_f). Our objectives were to determine (1) the extent to which this region acts as a catchment for individuals from across a species’ breeding range, (2) if temporal patterns of arrival arise as a function of migration distance inferred from δ ²H_f, and (3) if phenological differences among species segregate populations. The Darién concentrated populations of 6 species, with individuals potentially derived from 78% to 94% of their respective North American breeding ranges. The catchment area for the remaining 5 species covered 40–72% of breeding ranges, with a bias in origin from the west (e.g., Northern Waterthrush [Parkesia noveboracensis], Swainson’s Thrush [Catharus ustulatus]), north or center (Yellow Warbler [Setophaga petechia]) of their range. Differential timing in the migration of populations occurred in 6 species, generating a degree of temporal segregation. In contrast, peak migration for all species occurred in October, resulting in high overlap among species in their use of the Darién. Overall, our results describe high mixing of populations in the Darién for several species, which, given the region’s highly restricted geographic extent, suggests that a bottleneck effect occurs; however, comparisons with other regions in Central America and northern South America are required. The combination of extensive population mixing and limited temporal segregation over a narrow geographical area suggests that long-distance migrants may be especially vulnerable to events occurring in such regions, including adverse weather conditions and anthropogenic land cover change.

中文翻译：

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定义地理瓶颈的汇水来源：种群混合和物候重叠对新热带候鸟保护的意义

迁徙瓶颈使来自广泛繁殖地区的近北向新移民的个体和种群集中。这种集中发生的程度对于解释迁徙连通性和整个年度周期中的人口易受害性具有重要影响，但是对这种现象的研究很少。我们推断繁殖的11种在达连区域，西北哥伦比亚秋天迁移期间捕获新北区-新热带移民的起源，使用羽毛稳定氢同位素值（δ  ² ħ _˚F）。我们的目标是确定（1）在本区域充当用于从跨物种的育种范围的个体集水的范围内，（2）如果到达的时间模式的出现从δ推断迁移距离的函数的 ² ħ _˚F， （3）物种之间的物候差异是否将种群隔离。达里恩（Darién）集中了6种种群，其个体可能来自其各自北美繁殖范围的78％至94％。其余5种的集水区覆盖了40-72％的繁殖范围，起源于西部（例如北部水Water [ Parkesia noveboracensis ]，斯文森氏鹅口疮[ Catharus ustulatus ]），北部或中部（黄莺[ Yarlow Warbler [狗尾草]）的范围。种群迁移的时间差异有6种，产生了一定程度的时间隔离。相反，所有物种的迁徙高峰发生在10月，导致使用达里恩的物种之间高度重叠。总体而言，我们的研究结果描述了达里恩（Darién）几种物种的高度混合，鉴于该地区的高度地理范围，这表明出现了瓶颈效应。但是，需要与中美洲和南美洲北部的其他地区进行比较。广泛的人口混合和在狭窄的地理区域内有限的时间隔离的结合表明，长途移民可能特别容易受到此类地区发生的事件的影响，包括恶劣的天气条件和人为的土地覆盖变化。