Influence of weather on dragonfly migration and flight behaviour along the Baltic coast

Despite mass movements of dragonflies being documented for decades, the influence of weather on the movement decisions and movement intensity of dragonflies has rarely been studied. Here, we investigate the influence of local weather conditions on flight behaviour of dragonflies in Europe, taking advantage of large movements of dragonflies occurring along the Baltic Sea coast of Latvia. Firstly, we performed orientation tests with individual dragonflies of two commonly captured species, Aeshna mixta and Sympetrum vulgatum, in order to determine if dragonflies showed directed flight and whether flight direction was independent from wind direction. Aeshna mixta displayed a uniform mean southward orientation (166.7°), independent from prevailing wind directions, whereas S. vulgatum did not show a uniform orientation. Secondly, we investigated the influence of weather conditions on the abundance of dragonflies captured. Behavioural differences in relation to weather conditions were observed between A. mixta and the two smaller Sympetrum species (S. vulgatum and S. sanguineum). Generally, temperature, cloud cover and wind direction were the most important predictors for migration intensity, with temperature positively influencing abundance and cloud cover negatively influencing abundance. Aeshna mixta appeared to select favourable tailwinds (northerlies), whereas hourly abundance of Sympetrum increased with more easterly winds. Our results provide important information on the influence of local weather conditions on the flight behaviour of dragonflies, as well as evidence of migration for A. mixta and most likely some Sympetrum species along the Baltic coast.