Most research on song complexity has mainly focused on repertoire size. However, the way various song structures within a repertoire function in male-male interactions is less well understood. In this study, I have explored the functional significance of songs containing a trilled syllable type shown to have a clear maximum physiological performance barrier versus songs that lack a trilled element. I performed playback experiments with 44 song sparrows on the campus of Western Carolina University in North Carolina. I found that males responded significantly more strongly to trilled than non-trilled songs, suggesting that song sparrows discriminate between song types within a repertoire. The results of this study suggest that male-male interactions may be important drivers for the evolution of complex repertoires in song sparrows. Future studies should focus on understanding how trilled and non-trilled songs function in male-male interactions.