In lowland Neotropical regions, where air temperature and day length remain relatively constant year-round, seasonality is determined primarily by changes in rainfall. The wet season triggers the start of breeding for many Neotropical birds, but also alters the antigenic environment, likely increasing the risk of disease transmission. We explored two hypotheses about temporal variation in constitutive innate immunity of a Neotropical bird, the House Wren (Troglodytes aedon). One hypothesis proposes that Neotropical wrens up-regulate their immune function in the wet season either in anticipation of or in response to vectors that become more prevalent. A second hypotheses proposes that during periods of putative high resource demand, such as when parents are feeding young, immune function would be compromised and downregulated. Controlling for reproductive stage, we found that microbicidal capacity of blood against Escherichia coli was higher in the wet than the dry season, consistent with the antigen response hypothesis. Phagocytosis of E.coli and Staphylococcus aureus did not differ between wet and dry seasons. Microbicidal capacity and H/L-ration of tropical House Wrens did not vary among reproductive stages, and our data offered no support for the idea that immune function is compromised during the period when parents are feeding young.