Many animals repeat standardized displays multiple times while attracting a mate or deterring a rival. In such contexts it is possible that the ability to perform each display or signal type in a consistent fashion is under direct selection. Studies on sexual selection on song learning in birds have focused on differences in repertoire size with less attention to the potential importance of being able to perform each song/syllable type with high consistency. We present evidence that tropical mockingbirds decrease the variation between renditions of each syllable type as they grow older (i.e., become more consistent) and that more consistent males in this species tend to have higher dominance status and reproductive success. These findings stress the importance of consistency in the performance of sexual displays and suggest that this parameter may be very relevant even in species that are selected for high vocal diversity (i.e., large repertoires). In addition to signalling dominance status and age, we hypothesize that syllable type consistency may also be an indicator of the integrity of brain function in birds analogous to the tests used for neuropsychological assessment in humans.