Element concentrations in nestling tree swallows (Tachycineta bicolor) from the U.S. and Binational Great Lakes’ Areas of Concern: Data

Tree swallow, Tachycineta bicolor, nestlings were collected from 76 sites in the Great Lakes which included multiple sites at 27 Areas of Concern (AOCs) and 12 sites not listed as AOCs from 2010 to 2015. Livers were harvested and analyzed for 21 elements. Mercury concentrations differed among AOCs; however, all livers analyzed had concentrations well within background and generally comparable or lower than most sites outside of the Great Lakes. Mercury, the only element specifically identified in the designation of AOCs, does not seem to pose a threat to birds at any of the AOCs monitored. In contrast, selenium (Se) concentrations were elevated at sites on the southwest shore of Lake Michigan to levels that could be harmful to reproduction. Other toxic elements were elevated at selected AOCs, but the concentrations were not at toxic levels. Multivariate analysis identified concentration pattern differences among 8 AOCs that had 3 or more sites sampled. Of 29 possible AOC comparisons, 11 were significant and clear differences in patterns were evident. Concentration patterns of sites within AOCs appeared closely associated with one another. Additionally, Se was the primary contributor to the differences among the 8 AOCs for 9 of the 11 comparisons.