Analysis of Hg and Stable Isotope Concentrations in Bald Eagle Feathers from the Great Lakes and Voyageurs National Park, Minnesota

Bald eagles (Haliaeetus leucocephalus) feed on a variety of aquatic and terrestrial wildlife. As top predators in their food chain, they may accumulate harmful concentrations of pollutants such as mercury, which can have detrimental effects on populations of this species. The stable isotope composition of feathers provides useful information about the food resources assimilated by bald eagles. The connection between mercury, (Hg), concentration and stable isotope concentration ( 13C and 15N) of feathers were measured to better understand the potential sources and pathways of Hg uptake by bald eagles living in the Great Lakes region of Michigan and Voyageurs National Park (VNP), Minnesota in two related research projects. A third project that evaluated the spatial and temporal exposure of nestling bald eagles across Michigan was also conducted. In the first project, adult bald eagle feathers were collected from around the nesting sites in the Lower Peninsula (LP) and Upper Peninsula (UP), Michigan and VNP in 2003 and 2004 to determine if parts and sections of the feather were chemically or isotopically distinct. When analyzing feathers for Hg, a combination of the webbing and rachis should be used instead of either part separately because the webbing has significantly greater Hg concentrations. There were significant differences in Hg concentrations found among the sections of the bald eagle feather. There was a significantly greater Hg concentration in bald eagle feathers analyzed from VNP compared with feathers from the UP and LP in Michigan. In the second project, feathers from nestlings from three lakes at VNP were analyzed from 2005. There was a significantly lower Hg concentration in feathers of nestling bald eagles from nests located along Lake Kabetogama compared with feathers from nestling bald eagles at Rainy and Crane/Sandpoint Lakes. 15N concentrations in feathers from eagles nesting along Rainy and Crane/Sandpoint Lakes differed significantly. In the final project, nestling feathers of bald eagles from Michigan collected in 1999-2003, were analyzed for Hg concentrations. We compared Hg concentrations between sex, among years of collection, and compared concentration to productivity/reproductive success among subunits at three geographic scales. There were significant differences in Hg concentrations between the watershed years of study, 1999- 2003 for all the geographic locations, with the years 2002 and 2003 having significantly lesser Hg concentrations. By performing this research, valuable information was obtained on developing appropriate methods for the analysis and interpretation of Hg in feathers. Potential exposure pathways for bald eagles to Hg in the environment, and spatial and temporal trends of Hg in the Great Lakes region and VNP have been found which can assist with future management and conservation of bald eagles