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

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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

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