Song performance improves with continued singing across the morning in a songbird

Abstract

Vocal performance – an animal's ability to produce physically challenging vocalizations – can reflect a signaller's overall condition and can be a reliable signal of quality. It has been suggested recently that songbirds improve vocal performance through recent practice during intense dawn singing. We tested whether recent practice improves vocal performance in swamp sparrows, Melospiza georgiana, a species for which the biomechanical constraints and biological implications of vocal performance are well established. We measured vocal deviation – a measure of performance – in 1527 songs recorded from 11 captive swamp sparrows, four of which were developmentally stressed as juveniles. Vocal performance improved across the morning as a function of both the cumulative number of songs previously performed and the time of day. Song types with introductory syllables showed greater improvement than more typical song types composed solely of trilled syllables, and across all song types, as song output increased, the average improvement in vocal performance also increased. However, males with high song output exhibited greater variability in vocal performance, suggesting that some individuals might experience fatigue in song production. Furthermore, birds that had been developmentally stressed as juveniles showed greater improvement over the morning than birds that were not stressed. If conspecifics attend to within-individual variation in vocal performance, then improvement in vocal performance over the course of a day may drive birds to sing early and often, although fatigue may limit the extent to which this advantage may be gained.