Double function of flight in Calopteryx splendens (Odonata: Calopterygidae) males

Different flight manoeuvres of males of Calopteryx splendens were analysed by means of slow-motion filming. The wingbeat frequencies of males flying in tandem were higher than those of single flying males. A male exhibited the highest frequencies when carrying a Blue Featherleg tandem over a distance of 20–25 cm. The widest range of variability of values of wingbeat frequencies were recorded in threatening flight, probably due to the simultaneous communicative function of the wings during that behaviour. The upstroke/downstroke ratio of the wings allows to draw conclusions on their aerodynamic effect. It was low in pursuing flight, which is when more thrust is needed, and it was high in flight with an additional load (a Featherleg tandem) when a lot of lift was necessary. Both sexes exhibited wing standstills during forward flight. In males, the variability of the duration of wing standstills was widest, probably due to the communicative function of their blue wings. Because males engage in threatening displays their flight was very irregular and unsteady. In contrast, females were much more regular in their flight, which may explain why they win most pursuit races with males.