Abstract

Annual cycle events may be interlinked, influence following annual cycle stages, and may alter performance of individuals. Such links, called carry-over effects, can explain individual variation in timing or reproductive success in migratory species. Identifying the key links affecting fitness may reveal the mechanisms of species population dynamics but the current evidence for the strongest carry-over effects is equivocal. Here, we aim to assess the carry-over effects in great reed warblers Acrocephalus arundinaceus, a long-distance migratory songbird, using 103 full-annual tracks from three European and two Asian breeding populations. Our results showed strong positive relationships within autumn and spring migration periods and buffering capacity of the non-breeding period preventing events to carry over between these periods. Moreover, we found no profound relation between the non-breeding habitat quality or seasonality (quantified using stable isotopes and remote sensing data) and the timing of spring migration. The strongest carry-over effects occurred in individuals from the southern European breeding population compared to the northern and the central European populations. A moderate relationship between the habitat seasonality during moult and the spring migration timing indicates the importance of the complete moult. The overall weak carry-over effects of non-breeding habitat conditions found in this study contrast with previous results and imply between-species differences in these crucial relationships. Moreover, the population-specific carry-over effects highlight the importance of multi-population approach and advise caution in interpretation of results from single-population studies. Finally, the carry-over effect from the moulting period indicates the significance of a so-far neglected link in the species.

Significance statement

Environmental conditions vary in space and time. Therefore, migratory species adjust the timing of migration in order to maximise their fitness. However, the links between annual cycle events in multiple populations and the consequences of environmental conditions outside the breeding range are scarcely known. In this study, we used tracking data of the great reed warbler, an insectivorous bird species breeding across western Eurasia and wintering in Africa, to study a complex system of links between annual events. We found that the strength of these links differed between geographically distinct populations but not between sexes. Moreover, harsh environmental conditions during moult delayed the timing of subsequent events. Our findings could help explain large-scale differences in population size changes observed in some species and highlight the importance of energetically demanding moult period for the life of migratory species. Finally, our results demonstrate the need for multi-population approach in studies on seasonal interactions.

中文翻译：

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特定人群对迁徙鸣禽的结转效应的评估

摘要

年度周期事件可能相互关联，影响随后的年度周期阶段，并且可能会改变个人的表现。这种联系称为遗留效应，可以解释迁徙物种在时间安排或生殖成功方面的个体差异。确定影响适应性的关键环节可能揭示物种种群动态的机制，但目前最强的残留效应证据尚不清楚。在这里，我们旨在评估大芦苇莺Acrocephalus arundinaceus的残留效应，一种长途候鸟，使用来自三个欧洲和两个亚洲育种种群的103条全年记录。我们的结果表明，在秋季和春季迁徙时期内存在强的正相关关系，非繁殖时期的缓冲能力可以防止事件在这两个时期之间延续。此外，我们发现非繁殖生境质量或季节性（使用稳定同位素和遥感数据量化）与春季迁徙时间之间没有深远的关系。与北欧和中欧种群相比，最强的残留效应发生在南欧育种种群的个体中。换羽期间栖息地的季节性与春季迁徙时间之间的适度关系表明了换羽的重要性。在这项研究中发现的非繁殖生境条件的总体微弱的残留效应与先前的结果形成对比，并暗示了这些关键关系中的种间差异。此外，针对特定人群的遗留效应凸显了多种群方法的重要性，并建议在解释单种群研究结果时要谨慎。最后，换羽期的残留效应表明了物种中迄今为止被忽略的联系的重要性。

重要性声明

环境条件在时空上有所不同。因此，迁徙物种会调整迁徙的时机，以使其适应性最大化。但是，鲜为人知的是多个种群的年度周期事件与繁殖范围以外的环境条件的后果之间的联系。在这项研究中，我们使用了伟大的芦苇莺（一种横跨欧亚大陆西部和非洲越冬繁殖的食虫性鸟类）的跟踪数据来研究年度事件之间的复杂系统。我们发现，这些联系的强度在地理上不同的人群之间有所不同，但在性别之间没有差异。此外，换羽期间恶劣的环境条件延迟了后续事件的发生时间。我们的发现可以帮助解释某些物种中观察到的种群规模变化的大规模差异，并突出表明对于迁徙物种的生命充满活力地要求换羽期的重要性。最后，我们的结果证明了在季节性相互作用研究中需要采用多种群方法。