Flies exploit predictable perspectives and backgrounds to enhance iridescent signal salience and mating success

Communication requires both the encoding of information and its effective transmission, but little is known about display traits that primarily serve to enhance efficacy. Here we examined the visual courtships of Lispe cana, a cursorial fly that lives and mates in heterogeneous foreshores, and tested the prediction that males should seek to enhance signal salience and consequent fitness through the flexible choice of display locations. We show that courting males access the field of view of females by straddling them and holding their wings closed, before moving ahead to present their structurally coloured faces in ritualised dances. Males preferentially present these UV-white signals against darker backgrounds, and the magnitude of contrast predicts female attention, which in turn predict mating success. Our results demonstrate a striking interplay between the physical and attentional manipulation of receivers and reveal novel routes to the enhancement of signal efficacy in noisy environments.