Multimodal signalling in a songbird: male audiovisual displays vary significantly by social context in brown-headed cowbirds

Male brown-headed cowbirds, Molothrus ater, have repertoires of two to eight perched song types that are typically accompanied by a visual ‘wing-spread’ display when directed at male or female conspecifics. These physiologically demanding song displays are often produced in long bouts and are known to be important in intra- and intersexual interactions and to affect male mating success. The acoustic component of these multimodal signals has been extensively studied, but there is little or no published data on the visual part of these displays. We made audiovisual recordings of males (N = 9) directing song displays at male and female conspecifics, and based on inspection of playback of these recordings, we identified five major visual components of the display and quantified variation in these components using a scoring system. We calculated total display scores for male- and female-directed displays and found significant differences based on social context, with the most intense displays being directed at males. The extent of differences in display scores suggests that male- and female-directed displays may represent distinct signals and not a single signal of varying intensity. Although we are the first to report and quantify these differences, they are not unexpected because other than in the context of species identification, the function and information content of male- versus female-directed sexual signals are not predicted to be congruent.