The production of certain vocal signals in birds, such as food and alarm calls, is potentiated by the presence of an appropriate audience, and reduced when the signaller is alone. In this study, it is shown that the potentiating effects of a female chicken, Gallus domesticus, on the production of aerial alarm calls by a cockerel can be perfectly replicated by substituting the video image of a hen, with soundtrack, for a live vocalizing hen. The potentiating effect of a live conspecific audience is greater than that of a live bobwhite quail, Colinus virginianus, which is in turn more effective than an empty cage. Similarly, a hen videotape with sound is more effective than a bobwhite videotape with sound, which is in turn more effective than a videotape of an empty cage. A second experiment, using various combinations of the optical and sound tracks of videotapes, revealed that stimulation by both sensory modalities contributes to the audience effect. In this situation, visual and auditory cues play roughly equivalent roles. These experiments open up new prospects for the analysis of processes of visual communication in birds. For example, a domestic hen is normally more active than a bobwhite quail. By selecting bobwhite videotapes with high activity rates, it is demonstrated that the species specificity of the audience effect persists with activity rates reversed in favour of the heterospecific stimulus.