Syllable type consistency is related to age, social status and reproductive success in the tropical mockingbird

Many animals repeat standardized displays multiple times while attracting a mate or deterring a rival. In such contexts the ability to perform each display or signal type in a consistent fashion may be under direct selection. Studies on sexual selection on song learning in birds have focused on differences in repertoire size with less attention paid to the potential importance of being able to perform each song/syllable type with high consistency. We investigated whether syllable type consistency is related to age, social dominance and reproductive success in tropical mockingbirds, Mimus gilvus. The variation between renditions of each syllable type decreased as the birds grew older (i.e. they became more consistent). In addition, more consistent males tended 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). We hypothesize that, in addition to signalling dominance status and age, syllable type consistency may also indicate the integrity of brain function in birds analogous to the tests used for neuropsychological assessment in humans.