Summary Many Afro-Palearctic songbird migrants have declined, with conservation efforts mainly focused on the restoration of breeding habitat. However, pressures outside the breeding season might play a role. This includes the possibility that local relict populations no longer maintain the original phenotypic variation in migration patterns, with a loss of flexibility. The Great Reed Warbler Acrocephalus arundinaceus kept stable population levels in central and eastern Europe, but was almost extinct in the western part of the breeding range. In the Rhine delta the population declined from 10,000 individuals around 1950, to fewer than 100 at present. Here we document migratory timing, routes, and destinations of members of this remnant songbird population. It turned out that the remaining adults still showed high diversity in migratory phenotypes. This is even true in each of the two last tiny subpopulations in the Netherlands (of 50 and 15 pairs). So, even very small populations maintain the possible adaptive phenotypic variation, and with hindsight this justifies the breeding habitat restoration efforts currently underway.

中文翻译：

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莱茵河三角洲残余大芦苇莺种群在迁徙时间、停留地点和冬季目的地方面保持高度多样性


摘要 许多非洲-古北区鸣禽迁徙数量已经减少，保护工作主要集中在繁殖栖息地的恢复上。然而，繁殖季节以外的压力可能会产生影响。这包括当地孑遗种群不再保持迁徙模式的原始表型变异，从而失去灵活性的可能性。大芦苇莺Acrocephalus arundinaceus在中欧和东欧保持稳定的种群数量，但在繁殖范围的西部几乎灭绝。莱茵河三角洲的人口从 1950 年左右的 10,000 只下降到目前的不足 100 只。在这里，我们记录了这些残余鸣禽种群成员的迁徙时间、路线和目的地。事实证明，剩下的成虫在迁徙表型上仍然表现出高度的多样性。甚至在荷兰最后两个微小亚群（50对和15对）中也是如此。因此，即使非常小的种群也能维持可能的适应性表型变异，事后看来，这证明了目前正在进行的繁殖栖息地恢复工作的合理性。