During spring and fall billions of birds migrate through the night. It is widely recognized most nocturnal migrants start migrating around sunset. However, the timing of migration throughout the night has been studied less frequently. In Kranstauber at al. (2023), we analyze 3051 nights where migration was observed across 55 different weather radars in Europe. We find that most variation in the timing of migration throughout the night can be explained by an univariate axis.
In spring migration is generally evenly spread throughout the night compared to fall, furthermore closer to the coast migration is more concentrated at the beginning of the night. At these locations, birds either embark on sea crossings early in the night or continue migration one more days after a sea crossing at night fall. Understanding these patterns helps to optimize conservation and mitigation measures.