Effects of Metals in Birds
Metals have been responsible for some large-scale avian mortality events. These include mercury poisoning of seed-eating birds and their predators from mercurial fungicide-treated grain, lead poisoning of waterfowl and vultures from ingested shot, and selenium poisoning of waterbirds from agricultural wastewater (references in Chapter 1). In this chapter, we focus on lead, mercury, cadmium, selenium, chromium, manganese, and arsenic, and examine their effects on birds, as well as explaining the rationale for the elements we chose to study. These are circled in the periodic table (see Appendix Figure 9A.1 at end of this chapter), while the parallelogram denotes the elements that are considered heavy metals. We examine laboratory and field experiments, and their relevance to metal levels in Barnegat Bay and the other Northeast estuaries. In our studies of waterbirds, many of which are listed as threatened or endangered, it was necessary to rely on sampling that did not require killing the birds. We collected eggs and fledgling feathers. For each of the elements we analyzed, we searched for published effect levels, toxic thresholds, or data from which effect levels in eggs or feathers could be estimated. Metals in eggs served both as biomarkers of maternal exposure and chick exposure, but also as a direct source of toxicity to the embryo. Metal levels in feathers served as a biomarker of exposure for the developing bird during the several weeks of its prefledging growth.