The influence of colony habitat and egg components on lead and cadmium concentrations of great egrets and roseate spoonbills in southern Brazil

Birds are important sentinels of environmental contamination due to their well-known response to fluctuations in the concentration of trace elements and foraging preferences. Lead (Pb) and cadmium (Cd) are environmental contaminants that can cause lethal or sublethal effects, such as neurological, physiological, and reproductive dysfunction in a range of bird species. Here, we examined Pb and Cd concentrations in eggshells and egg contents of great egrets (Ardea alba) and roseate spoonbills (Platalea ajaja), waterbirds with contrasting foraging strategies, from two habitats, estuarine and limnetic, in southern Brazil. We found that colony habitat had an important influence on Pb and Cd concentrations in eggshells, confirming that environmental abiotic factors play a role in the uptake and bioavailability of these elements. Great egrets had higher Pb concentrations in eggshells and egg contents in the estuary habitat, as well as higher Cd in egg contents at the limnetic colony compared to roseate spoonbills. Contrastingly, spoonbills from the limnetic habitat had the highest Pb concentrations. Differences in concentrations of Pb and Cd among breeding sites and egg components may be related to the distinct foraging sites by females of egrets and spoonbills before the egg laying. Our results indicate ongoing estuarine and freshwater contamination by Pb and Cd in southern Brazilian coastal areas. Indeed, Cd concentrations in waterbirds were higher than the environmental standards, which is a concern for wildlife health and environmental quality. Finally, eggshells proved to be a sensitive, efficient, and low-impact sampling method to monitor low levels of contamination in waterbirds.