Migrant birds travel between their breeding areas and wintering grounds by alternating energetically and physiologically demanding flights with periods of rest and fuelling, so-called stopovers. An important intrinsic factor influencing the decision to resume migration is the amount of energy stores available for the next flight. Correlative studies with free-flying birds and experimental studies with caged birds have shown that the amount of energy stores affects the day-to-day, within-day and the directional decision of departure. The methodological advantages of both the correlative and experimental approach are combined when radio-tagging many individuals on the same day and subsequently determining the departure decisions at a high spatiotemporal resolution. Making use of such a quasi-experimental approach with an automated radio-tracking system at stopover, we studied the effect of energy stores on departure decisions and whether they vary between species of different migration strategies experiencing contrasting time constraints. For this, we chose a long-distance migrant, the common redstart (Phoenicurus phoenicurus), and a medium-distance migrant, the European robin (Erithacus rubecula), because the former has to travel at relatively higher speed to reach its wintering ground in a reasonable time at the expense of relatively higher energetic costs for travelling than the latter. Common redstarts with higher energy stores were more likely to resume migration than their conspecifics with lower energy stores, whereas this pattern was absent in the European robins. The amount of energy stores significantly affected the timing of departure within the day, with large energy stores yielding early departures in both species. Departure directions from the stopover site during the first night after capture were oriented towards the seasonally appropriate direction but were not affected by variation in energy stores. We demonstrate the importance of variation in energy stores on the departure decisions and that it may affect species with different migration strategies dissimilarly in autumn. Nevertheless, knowledge of other intrinsic factors, such as feeding conditions, health status and physiological consequences of previous flights, is additionally required to better understand the departure decisions of migrants, as this is the key to providing an overall assessment of the decision-making process.

中文翻译：

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一种使用遥测技术评估中途停留决策过程中迁移策略特定差异的准实验方法。

候鸟通过在精力和生理上需要交替的飞行以及休息和加油（所谓的中途停留），在繁殖区和越冬场之间旅行。影响决定恢复迁移的一个重要内在因素是下一次飞行可用的能量存储量。对自由飞行鸟类的相关研究和对笼养鸟类的实验研究表明，能量存储的量会影响日常，日内以及出发的方向。当在同一天对许多人进行无线电标记并随后以高时空分辨率确定出发决策时，相关方法和实验方法的方法学优势都得到了结合。通过在中途停留时使用这种带有自动无线电跟踪系统的准实验方法，我们研究了能量存储对出发决策的影响，以及它们在经历相对时间限制的不同迁移策略的物种之间是否有所不同。为此，我们选择了长途迁徙的普通红尾（（Phoenicurus phoenicurus）和中途迁徙的欧洲知更鸟（Erithacus rubecula），因为前者必须以相对较高的速度行进才能到达其越冬地。一个合理的时间，但要付出比后者更高的精力成本。具有较高能量存储的普通鱼比具有较低能量存储的同种鱼更可能恢复迁徙，而欧洲知更鸟没有这种模式。能量存储的数量显着影响一天中离开的时间，大型能量存储使这两个物种都提前离开。在捕获后的第一个晚上从中途停留地点出发的方向朝向季节性适当的方向，但不受储能变化的影响。我们证明了储能变化对离开决策的重要性，并且它可能在秋季以不同的迁移策略影响物种。但是，还需要了解其他内在因素，例如进食条件，健康状况和以前的航班的生理后果，以更好地了解移民的离境决定，因为这是对决策过程进行全面评估的关键。