MERCURY CONCENTRATIONS IN TISSUES OF FLORIDA BALD EAGLES

We collected 48 blood and 61 feather samples from nestling bald eagles (Haliaeetus leucocephalus) at 42 nests and adult feather samples from 20 nests in north and central Florida during 1991-93. We obtained 32 liver, 10 feather, and 5 blood samples from 33 eagle carcasses recover ed in Florida during 1987-93. For nestlings, mercury concentrations in blood (GM = 0.16 ppm wet wt) and feather (GM = 3.23 ppm) samples were correlated (r = 0.69, P = 0.0001). Although nestlings had lower mercu ry concentrations in feathers than did adults (GM = 6.03 ppm), the fea ther mercury levels in nestlings and adults from the same nest were co rrelated (r = 0.63, P < 0.02). Mercury concentration in blood of capti ve adult eagles (GM = 0.23 ppm) was similar to Florida nestlings but s ome Florida nestlings had blood mercury concentrations up to 0.61 ppm, more than twice as high as captive adults. Feather mercury concentrat ions in both nestlings and adults exceeded those in captive eagles, bu t concentrations in all tissues were similar to, or lower than, those in bald eagles from other wild populations. Although mercury concentra tions in Florida eagles are below those that cause mortality, they are in the range of concentrations that can cause behavioral changes or r educe reproduction. We recommend periodic monitoring of mercury in Flo rida bald eagles for early detection of mercury increases before negat ive effects on reproduction occur.