Data from: Solar heating may explain extreme diel flight altitude changes in migrating birds

Great reed warblers Acrocephalus arundinaceus and great snipes Gallinago media exhibit a diel cycle in flight altitudes, flying much higher during day than night, when performing migratory flights covering both night and day (Fig 1). One hypothesis proposed to explain this behaviour is that the birds face additional heating by solar radiation during daytime and hence must climb to very high, and thus also very cold, altitudes to avoid overheating during daytime flights. Yet, solar heat gain in birds has been shown to drastically decrease with wind speed, and the quantitative heating effect by solar radiation on a bird flying with an airspeed of 10 m/s or more, is unknown. We analysed temperature data from multisensor data loggers placed without direct exposure to solar radiation on great reed warblers (the logger covered by feathers on the back) and great snipes (the logger on the leg, covered from the sun by the tail). We found that logger temperatures were significantly higher (5.9–8.8 °C in great reed warblers and 4.8–5.4 °C in great snipes) during the day than during the night, in birds flying at the same altitudes (and thus also the same expected ambient air temperatures; Tables 1, 2; Fig 2). These results strongly indicate that the heat balance of the flying birds is indeed affected by solar radiation, which is in accordance with the hypothesis that solar radiation is a key factor causing the remarkable diel cycles in flight altitude observed in these two long-distance migrant bird species. This dataset contains all data included in the figures and analyses included in the published paper: Sjöberg et al., Solar heating may explain extreme diel flight altitude changes in migrating birds, Current Biology (2023), https://doi.org/10.1016/j.cub.2023.08.035大苇莺（Great reed warblers，Acrocephalus arundinaceus）与大沙锥（great snipes，Gallinago media）的飞行高度存在日周期性变化（diel cycle）：在跨昼夜的迁徙飞行过程中，它们日间的飞行高度远高于夜间（图1）。针对这一行为，有研究者提出假说：鸟类在日间会受到太阳辐射带来的额外热负荷，因此必须攀升至极高且低温的高空，以避免日间飞行时出现过热问题。然而现有研究表明，鸟类的太阳热增益会随风速升高而大幅降低，但当鸟类以10 m/s及以上的空速（airspeed）飞行时，太阳辐射对其产生的定量热效应仍不明确。我们对安装在两种鸟类身上、未直接暴露于太阳辐射下的多传感器数据记录仪（multisensor data loggers）的温度数据进行了分析：其中大苇莺的记录仪固定于背部，被羽毛覆盖；大沙锥的记录仪固定于腿部，被尾部遮挡阳光。在飞行高度相同（因此预期环境气温也一致；表1、表2；图2）的个体中，我们发现日间记录仪温度显著高于夜间：大苇莺的温差为5.9–8.8 °C，大沙锥为4.8–5.4 °C。上述结果强烈表明，飞行鸟类的热平衡确实会受到太阳辐射的影响，这与"太阳辐射是导致这两种长途迁徙鸟类出现显著飞行高度日周期性变化的关键因素"的假说相符。 本数据集包含该已发表论文中所有附图及分析所用数据： Sjöberg 等，《太阳加热可解释迁徙鸟类极端的飞行高度日变化》，《当代生物学》（Current Biology，2023），https://doi.org/10.1016/j.cub.2023.08.035