Directional communication, that is, the use of body orientation to increase signal transmission, has been widely neglected in studies of animal communication. Here I propose that the experimental study of singing direction in birds can provide insights into the function of song. I studied two populations of sedge warblers in Britain and Germany. In this species, song is thought primarily to be a mate attraction signal, as males cease to sing once they are paired. However, using a combination of playback experiments and behavioural observation, I found that males approach a playback loudspeaker simulating a rival male and also orient themselves towards the loudspeaker while singing. This finding shows that sedge warbler songs are also directed at rival males and that the dual function of mate attraction and territory defence is hidden from the human observer because singing ceases after pairing. I found the study of directed communication to be a powerful tool in addressing functional questions, provided the analysis is conducted with statistical methods for data from circular distributions. In conclusion, I advocate that animal orientation should be taken into account when conducting investigations of signalling behaviour.