The apparent paradox posed by the synchronization of mating displays by males competing to attract females has provoked considerable interest among evolutionary biologists1,3. Such synchronized sexual signalling has only been documented for communicationusing light flashes (bioluminescence) or sound. It has been suggested that the “fundamental reasons that might favour precise adjustments in signal timing relative to that of a particular neighbour could only be compelling for signallers using these two channels”1. Here we provide the first quantitative evidence for synchronous production of a conventional visual courtship signal, the movement of a body part.