Identifying the forces driving seasonal rhythms in zoonotic disease risk are necessary to effectively target mitigation efforts, though drivers that persist across distinct environments remain to be described. As the capacity for a host to transmit a pathogen (i.e. competence) is predominantly governed by the immune system (e.g., the duration and magnitude of infectiousness), broad trends in reservoir immune defenses ought to be a central driver of disease seasonality, though this assumption has yet to be examined. To investigate the magnitude of seasonal variation in reservoir immune defenses and the forces driving these rhythms, I performed a series of West Nile virus (WNV) infections in a ubiquitous reservoir. House sparrows (Passer domesticus) were captured in the Tampa Bay area and experimentally exposed to WNV across key life history stages. Over the course of infection, I quantified viremia and expression of key modulators of the inflammatory immune response, IFNγ and TNFα. As host immune defenses are modulated through dynamic energy allocation, I hypothesize that competence will be intimately linked to host physiological state, where those infected during times of great energetic demand, (e.g., reproduction and molt) maintain infectiousness for an extended length of time. Furthermore, I predict that life history tradeoffs manifest through reduced expression of the chosen biomarkers of WNV resistance. If these hypotheses are supported, the results from this study will demonstrate seasonal rhythmicity of functional immune defenses in a key disease reservoir and a potentially pervasive driver of zoonotic disease seasonality.