Indicator models of sexual selection predict that ornaments may reliably advertise male quality and in particular, viability. Songbird song is a well-studied ornament used by females to evaluate potential mates. In this thesis I examine the reliability of two different aspects of song, thought to develop over different timescales, in indicating immune function of breeding male song sparrows [Melospiza melodia). Immunity was assessed through multiple measures of constitutive innate immune function. Overall, I observed a pattern of constitutive immunity that suggests within- system trade-offs. Moreover, this pattern was associated with measures of song complexity. Male song sparrows with more complex song had significantly higher levels of circulating protective proteins (natural antibody, haptoglobin and lysozyme), but showed decreased levels and/or activity of peripheral blood cellular immunity. I observed no significant association between measures of song stereotypy and constitutive immune function. Ultimately, this study suggests that song complexity (although not song stereotypy) may be associated with individual variation in self-maintenance strategies, rather than a simple indicator of quality as originally hypothesize
