The cooperatively breeding superb fairy-wren, Malurus cyaneus, sings two types of song; a variable, complex song sung by both sexes, and a relatively invariant, stereotyped song sung only by males. Field observations and playback experiments revealed that the male song could be triggered by a variety of loud avian and non-avian vocalizations, but was triggered most frequently by the calls of predators or potential predators. The male song is sung both within the territory and in winter feeding flocks outside the territory. Acoustic properties of the song suggest that it is a long-range signal. A possible explanation for this unusual phenomenon is that the male song has evolved through sexual selection as an honest signal to females of male quality, for the purpose of obtaining extra-pair copulations.