Signal Interception and the Use of Soft Song in Aggressive Interactions

Many species of songbirds produce songs of unusually low amplitude during aggressive encounters (Dabelsteen et al. 1998); such low amplitude songs have been variously termed ‘soft songs’ (Nice 1943), ‘strangled songs’ (Snow 1958), and ‘quiet songs’ (Dabelsteen et al. 1998). In some species, soft songs are produced in courtship as well as in aggression, but in our study species, the song sparrow (Melospiza melodia), soft songs have been noted only in aggressive contexts (Nice 1943; Beecher et al. 2000). Some birds are known to increase song amplitude when interacting with another male (Brumm & Todt 2004), which seems the logical strategy if the function of the signal is to intimidate a rival. By contrast, decreasing amplitude in an aggressive contest seems somewhat paradoxical. One way to escape the paradox is to suppose that soft song actually has a submissive message rather than an aggressive one; Correspondence William A. Searcy, Department of Biology, University of Miami, Coral Gables, FL 33124, USA. E-mail: [email protected]