Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom.
PLoS One. 2012;7(4):e34542. doi: 10.1371/journal.pone.0034542. Epub 2012 Apr 5.
Winter habitat use and the magnitude of migratory connectivity are important parameters when assessing drivers of the marked declines in avian migrants. Such information is unavailable for most species. We use a stable isotope approach to assess these factors for three declining African-Eurasian migrants whose winter ecology is poorly known: wood warbler Phylloscopus sibilatrix, house martin Delichon urbicum and common swift Apus apus. Spatially segregated breeding wood warbler populations (sampled across a 800 km transect), house martins and common swifts (sampled across a 3,500 km transect) exhibited statistically identical intra-specific carbon and nitrogen isotope ratios in winter grown feathers. Such patterns are compatible with a high degree of migratory connectivity, but could arise if species use isotopically similar resources at different locations. Wood warbler carbon isotope ratios are more depleted than typical for African-Eurasian migrants and are compatible with use of moist lowland forest. The very limited variance in these ratios indicates specialisation on isotopically restricted resources, which may drive the similarity in wood warbler populations' stable isotope ratios and increase susceptibility to environmental change within its wintering grounds. House martins were previously considered to primarily use moist montane forest during the winter, but this seems unlikely given the enriched nature of their carbon isotope ratios. House martins use a narrower isotopic range of resources than the common swift, indicative of increased specialisation or a relatively limited wintering range; both factors could increase house martins' vulnerability to environmental change. The marked variance in isotope ratios within each common swift population contributes to the lack of population specific signatures and indicates that the species is less vulnerable to environmental change in sub-Saharan Africa than our other focal species. Our findings demonstrate how stable isotope research can contribute to understanding avian migrants' winter ecology and conservation status.
冬季栖息地利用和迁徙连通性的程度是评估鸟类迁徙者数量明显下降的驱动因素的重要参数。对于大多数物种来说，这些信息是不可用的。我们使用稳定同位素方法来评估三种非洲-欧亚大陆迁徙鸟类的这些因素，它们的冬季生态学知之甚少：林莺 Phylloscopus sibilatrix、家燕 Delichon urbicum 和普通雨燕 Apus apus。在空间上分隔的繁殖林莺种群（在 800 公里的横断面上进行采样）、家燕和普通雨燕（在 3500 公里的横断面上进行采样）在冬季生长的羽毛中表现出统计学上相同的种内碳和氮同位素比值。这种模式与高度的迁徙连通性兼容，但如果物种在不同地点使用同位素相似的资源，也可能出现这种模式。林莺的碳同位素比值比典型的非洲-欧亚大陆迁徙者更贫化，与使用湿润的低地森林兼容。这些比值的非常有限的方差表明，它们对同位素限制资源的专门化，这可能导致林莺种群稳定同位素比值的相似性，并增加其越冬地对环境变化的敏感性。家燕以前被认为主要在冬季使用湿润的山地森林，但考虑到家燕碳同位素比值的富集性质，这似乎不太可能。家燕比普通雨燕使用更窄的资源同位素范围，表明其专业化程度更高或越冬范围相对有限；这两个因素都可能增加家燕对环境变化的脆弱性。每个普通雨燕种群内同位素比值的显著差异导致缺乏种群特异性特征，并表明该物种在撒哈拉以南非洲比我们的其他焦点物种对环境变化的敏感性较低。我们的研究结果表明，稳定同位素研究如何有助于理解鸟类迁徙者的冬季生态学和保护状况。
