Migration is an important component of some species full annual cycle. California’s Central Valley and the Colorado River Delta provide important riparian and wetland habitats for migrating waterbirds in the arid west of North America, but little is known about whether these locations are important at the population level to migrating landbirds. We used eBird Status and Trends abundance data to quantify the importance of the Central Valley and Colorado River Delta to landbirds by estimating the proportion of the breeding population of 112 species that use each site during migration. We found that ~17 million landbirds use the Colorado River Delta in the spring and ~14 million in the fall. Across 4 study regions in the Central Valley, up to ~65 million landbirds migrate through in the spring and up to ~48 million in the fall. In the spring and fall, respectively, up to 37 and up to 30 species had at least 1% of their continental population migrate through the study regions. We also quantified the spatial concentration of each species across latitudinal transects to determine the extent to which study regions were acting as migratory bottlenecks. Landbird abundances were spatially concentrated in study regions 29.4% of all migration weeks, indicating that each study region acts as a migratory bottleneck. This application of eBird data is a powerful approach to quantifying the importance of sites to migrating birds. Our results provide evidence of population-level importance of the Central Valley and Colorado River Delta for many migratory landbirds.

中文翻译：

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科罗拉多河三角洲和加利福尼亚的中央山谷是许多北美陆鸟迁徙的关键地区

迁徙是某些物种全年循环的重要组成部分。加利福尼亚的中央山谷和科罗拉多河三角洲为北美干旱西部的迁徙水鸟提供了重要的河岸和湿地栖息地，但人们对这些地点在人口水平上对迁徙的陆鸟是否重要知之甚少。我们使用 eBird 状态和趋势丰度数据来量化中央山谷和科罗拉多河三角洲对陆鸟的重要性，通过估计在迁徙过程中使用每个地点的 112 个物种的繁殖种群的比例。我们发现春季约有 1700 万只陆鸟使用科罗拉多河三角洲，秋季则有约 1400 万只。在中央山谷的 4 个研究区域中，多达 6500 万只陆鸟在春季迁徙，秋季多达 4800 万只。在春天和秋天，分别有多达 37 个和多达 30 个物种有至少 1% 的大陆种群迁移通过研究区域。我们还量化了每个物种在纬度横断面上的空间浓度，以确定研究区域作为迁徙瓶颈的程度。陆鸟丰度在空间上集中在研究区域，占所有迁徙周的 29.4%，这表明每个研究区域都是迁徙瓶颈。eBird 数据的这种应用是量化地点对迁徙鸟类的重要性的有力方法。我们的研究结果证明了中央山谷和科罗拉多河三角洲对许多迁徙陆鸟的种群重要性。我们还量化了每个物种在纬度横断面上的空间浓度，以确定研究区域作为迁徙瓶颈的程度。陆鸟丰度在空间上集中在研究区域，占所有迁徙周的 29.4%，这表明每个研究区域都是迁徙瓶颈。eBird 数据的这种应用是量化地点对迁徙鸟类的重要性的有力方法。我们的研究结果证明了中央山谷和科罗拉多河三角洲对许多迁徙陆鸟的种群重要性。我们还量化了每个物种在纬度横断面上的空间浓度，以确定研究区域作为迁徙瓶颈的程度。陆鸟丰度在空间上集中在研究区域，占所有迁徙周的 29.4%，这表明每个研究区域都是迁徙瓶颈。eBird 数据的这种应用是量化地点对迁徙鸟类的重要性的有力方法。我们的研究结果证明了中央山谷和科罗拉多河三角洲对许多迁徙陆鸟的种群重要性。表明每个研究区域都是迁移瓶颈。eBird 数据的这种应用是量化地点对迁徙鸟类的重要性的有力方法。我们的研究结果证明了中央山谷和科罗拉多河三角洲对许多迁徙陆鸟的种群重要性。表明每个研究区域都是迁移瓶颈。eBird 数据的这种应用是量化地点对迁徙鸟类的重要性的有力方法。我们的研究结果证明了中央山谷和科罗拉多河三角洲对许多迁徙陆鸟的种群重要性。