Abstract: Within any given population, there exists a wide range of phenotypic variation between individuals. Often, variety within male phenotypes is used by females to judge male quality and can be used by researchers to predict reproductive success. Within songbirds, variation in male song performance can be used as a predictor of male quality and subsequently reproductive success. Male Dark-eyed Juncos ( Junco hyemalis ), a small North American songbird, typically sing a single, repeated, high-pitched trill. Due to motor constraints, a male's trill rate constrains its frequency bandwidth (range) and a “high performance” song is one in which the frequency bandwidth approaches the physiological limit for a given trill rate. Based on these motor constraints, a larger male should sing a higher performance song. This study investigated if A) junco song performance is correlated to reproductive success? and B) if junco song performance is correlated to other phenotypic measures of male quality? To test this I recorded the songs of 65 male juncos, measured various morphological characters, took blood samples, and tracked their nesting success over the course of a single breeding season. Results were not statisitically significant, but I noted a trend indicating that higher performance singers were larger males, yet they had lower apparent reproductive success than smaller, lower-performance singers. However, larger males are known to have higher actual reproductive success due to more extra-pair fertilizations and therefore I expect results of paternity analysis to demonstrate equal or higher reproductive success for high-performance singers.