The ecological and physiological costs of lead shot and immunological challenge to developing western bluebirds.
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We investigated the interacting effects of a nonpathogenic immunological challenge and exposure to lead shot early in the development of nestling western bluebirds (Sialia mexicana). Nestlings were randomly assigned to each of six treatments of an incomplete block design with two antigen treatments, Newcastle disease virus (NDV) or sheep red blood cells (SRBC), and four lead shot treatments (no shot, one shot--0.05 g, 2 shots--0.1 g, or three shots--0.15 g). Survival functions did not differ between the lead treatment groups, and there were no effects of lead treatments on weight, growth rates, fluctuating asymmetry (FA), or antibody response. NDV- and SRBC-treated birds survived better than control birds which may be due to an adjuvant-activation of the entire immune system. However, FA was greater in individuals in the NDV and SRBC treatment groups, suggesting a tradeoff between growth and immunocompetence. Cell-mediated response to phytohemagglutinin of the high-lead treatment groups was significantly less than other groups. Hematocrit increased with age and weight, and was not affected by lead or antigen. While in this study the shape of the growth curve, FA, cell-mediated immunity, and behavior were affected by the higher dose of lead shot, actual lead concentrations in blood are needed to verify this process. Antigenic stress was documented in nestling developmental stability and there were no measured effect of both the lead shot and immunological challenge in combination.