Cadmium and Lead Exposure Associated with Reduced Growth Rates, Poorer Fledging Success of Little Blue Heron Chicks (Egretta caerulea ) in South Louisiana Wetlands

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Persistent contaminants in ecosystems are often monitored via organisms that bioaccumulate the pollutant of interest. Several published studies have used colonial wading birds to assess contamination by heavy metals in aquatic ecosystems. Using a nonlethal sampling regimen, this study identified chick feathers and guano as tissues that best reflect local contamination. Both cadmium and lead were detected in food samples (0.3–4.3 μg/g Cd, 0.8–9.3 μg/g Pb), guano (0.2–3.2 μg/g Cd, 1.0–9.5 μg/g Pb), and feathers (0.6–25.4 μg/g Cd, 1.2–16.9 μg/g Pb) from little blue heron chicks at levels similar to other studies. Chicks exposed to cadmium had significantly slower growth rates than nonexposed chicks, and exposure to lead was correlated with increased nestling mortality. The appropriate scale of comparison necessary to demonstrate these effects and the usefulness of wading birds as bioindicators are discussed.