Avian spring migration at the east Adriatic coast: coastal and sea-crossing dynamics of intensity, timing, and flight directions

Simultaneous nocturnal bird migration across and along geographical barriers can lead to very complex spatiotemporal patterns of directions and intensity. Understanding these is necessary to coordinate dynamic conservation actions such as the temporal shut down of disturbing illumination or potentially harmful wind turbines. Previously, it was suggested that within-night timing of migrants is partially related to upstream geographical features. We used radar monitoring to record two years of spring migration to investigate these dynamics at the coast of Croatia. With FPCA and hierarchical clustering, we tried to disentangle the relationship between within-night timing of migration and related flight directions. However, our analysis has demonstrated that although distinct patterns have been observed over the season, within-night timing was not necessarily connected to a distinct preferred migration direction.