Abstract Migrating birds make stopovers to rest and fuel to prepare for their next flight. The decision when to continue migration significantly affects total duration of migration and thus arrival timing at the migratory destination. Departure decisions of migrants are therefore important to understand variation in arrival timing. Since the amount of energy can limit flight duration, feeding conditions and energy stores have a significant effect on the departure decisions. Unexpectedly though, various fasting-refuelling experiments controlling for these two parameters and using migratory restlessness as a proxy for departure probability did not find consistent patterns within and across different songbird species of departure decisions. Here we performed a fasting-refuelling experiment on four actively migrating songbird species during autumn, to assess the significance and consistency of the feeding conditions and energy stores on the bird’s departure decision. We found no differences in the departure probability between low and favourable feeding conditions in all species. During the low food phase, however, birds with higher energy stores were more likely to depart than leaner birds. When fasted individuals encountered improved feeding conditions, they significantly increased their energy stores and showed a significant drop in migratory restlessness. This is tantamount to the decision of staying at stopover. The consistency of the patterns seems to be generalizable across species. Additionally, the results highlight the importance of the interplay of feeding conditions, changes in these and the bird’s current energy stores for the stopover decision-making process. Significance statement Many migratory songbirds travelling thousands of kilometres do so by making several single nocturnal flights interrupted by resting periods on the ground. To decide when to continue migration, birds seem to follow general departure rules. Fat birds continue migration when they do not find food during their rest, while lean birds stay until the feeding conditions have improved. In this study, we show for the first time a generalizable consistent pattern that feeding conditions, changes in food availability and the current energy stores jointly influence the departure decisions of migratory songbirds at stopovers. This is in contrast to former studies showing inconsistent patterns on the reaction of a low food phase regarding the departure probability. Our experiment, therefore, advances our knowledge about the decision-making process of bird migrants and demonstrates the importance of favourable feeding conditions for migratory birds resting at a stopover site.

中文翻译：

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候鸟中途停留的决策：能量储存和觅食条件的相互作用

摘要 候鸟会在中途停留休息和加油，为下一次飞行做准备。何时继续迁移的决定会显着影响迁移的总持续时间，从而影响迁移目的地的到达时间。因此，移民的出发决定对于理解抵达时间的变化很重要。由于能量的数量可以限制飞行持续时间，喂食条件和能量储存对起飞决策有显着影响。然而出乎意料的是，控制这两个参数并使用迁徙不安作为出发概率代理的各种禁食-加油实验并未在不同鸣禽种类的出发决定内部和之间找到一致的模式。在这里，我们在秋季对四种活跃迁徙的鸣禽进行了禁食-加油实验，评估饲养条件和能量储备对家禽离开决定的重要性和一致性。我们发现所有物种的低摄食条件和有利摄食条件之间的离开概率没有差异。然而，在低食物阶段，能量储存较高的鸟类比瘦弱的鸟类更有可能离开。当禁食的个体遇到改善的进食条件时，他们的能量储存显着增加，并且迁徙的不安感显着下降。这无异于中途停留的决定。模式的一致性似乎可以跨物种推广。此外，结果强调了喂养条件、这些条件的变化以及家禽当前能量储存之间相互作用对中途停留决策过程的重要性。意义声明 许多迁徙的鸣禽通过在地面上休息时间中断几次单独的夜间飞行来飞行数千公里。为了决定何时继续迁徙，鸟类似乎遵循一般的出发规则。胖鸟在休息期间找不到食物时会继续迁徙，而瘦鸟则留在觅食条件改善之前。在这项研究中，我们首次展示了一种普遍一致的模式，即觅食条件、食物供应的变化和当前的能量储存共同影响候鸟在中途停留的出发决定。这与之前的研究形成对比，之前的研究显示低食物阶段对离开概率的反应模式不一致。因此，我们的实验，