Environmental contaminants in nestling Bald Eagles produced in Montana and Wyoming

Abstract

Upper-trophic level piscivores, such as Bald Eagles (Haliaeetus leucocephalus), may be at risk of exposure to environmental contaminants in the western United States from coal-fired power plants and coal-bed methane wells. We collected 64 blood samples from nestling Bald Eagles in southeastern Montana and northwestern Wyoming during 2007–08 for analyses of heavy metals, trace elements, and organochlorine compounds. Mercury was detected in all blood samples and averaged (±SD) 0.28 ± 0.20 ppm. Most nestlings (82.8%) had concentrations near expected background levels, but 7.8% had elevated (>0.7 ppm) mercury levels. Nestlings in Wyoming ( = 0.37 ± 0.22 ppm) had higher blood mercury concentrations than nestlings from Montana ( = 0.22 ± 0.17 ppm; t31 = 3.151, P = 0.015). In Montana, nestlings sampled on Yellowstone River tributaries had lower blood mercury concentrations ( = 0.12 ± 0.10 ppm) than nestlings from the main stem of the Yellowstone River ( = 0.28 ± 0.21 ppm) and Wyoming ( = 0.37 ± 0.22 ppm; F2,32 = 12.439, P < 0.001). Blood levels of mercury and selenium were positively correlated (rS = 0.281, n = 64, P = 0.024). Lead ( = 0.07 ± 0.08 ppm) was detected in 81.3% of nestlings, but only 11.5% of those were considered above background levels. The organochlorine p,p′-DDE ( = 0.003 ± 0.003 ppm) was detected in 69.6% of nestlings sampled. Compared to previous studies in the region, mercury contamination has become more widespread, whereas the prevalence of lead contamination was similar to that of the past. Based on this study, we suggest that some Bald Eagle nestlings may be experiencing adverse effects from mercury contamination, and recommend that additional monitoring take place as coal-fired power plants and the coal-bed methane industry continue to expand.