Abstract
Demanding performance of vocal signals, such as birdsong, may be evaluated by trade-offs among acoustic traits. If individuals differ in their ability to sustain physiologically demanding singing, then aspects of song performance resulting from such trade-offs could signal individual quality. Song performance can also differ among song types, and it is not known whether this influences the assessment of individual quality. We asked whether three trade-off-based measures of song performance indicate male age or aspects of condition (body condition, hematocrit and ectoparasite load) in the dark-eyed junco (Junco hyemalis), a species with small repertoires. Across a sample of over 100 males, no measure of song performance was related to male age or condition, nor did song performance improve with age for those males recorded in consecutive years. In all cases, the variation in song performance explained by these predictors was small (<4%). Instead, the more song types we recorded from a male, the more likely we were to record high-performance songs, and this sampling effect was stronger than putative correlations with male quality. These results complement a previous study on this population showing that most variation in performance is found among song types rather than among males. Collectively, the lack of association between trade-off-based aspects of song performance and male age or condition, plus variation among song types that interferes with rapid assessment of a male's best performance, indicate that these aspects of song performance do not allow a good assessment of male quality in juncos, and perhaps more generally in species with song repertoires.