Summary |
Bioaccumulation of mercury (Hg) in avian piscivores can result in diminished reproductive success. Local fish Hg consumption advisories and the osprey's sensitivity to contaminants prompted this investigation. Eggs, feather, and blood samples were collected during the 2003 and 2004 osprey nesting seasons at Lake Mattamuskeet in Hyde County, North Carolina, and the 2004 season at the Pamlico River in Beaufort County, North Carolina were analyzed for total Hg content. All eggs analyzed carried 0.06 ppm Hg or less. Pre-fledge osprey at Lake Mattamuskeet had significantly higher Hg body burdens and lower nesting success than those on the Pamlico River, an estuarine river within the same coastal basin. Lake nests (n = 11) had mean nest blood, down, and contour feather Hg values of 0.24 ppm ±0.16 ppm, 4.23 ppm ± 1.52 ppm, and 6.31 ppm ± 2.75 ppm, respectively. River nests (n = 9) had 0.11 ppm ± 0.06 ppm, 1.67 ppm ± 0.87 ppm, and 2.37 ppm ± 1.45 ppm, respectively. Hg levels in blood of osprey in the Pamlico River decreased with proximity to marine waters. Hg levels of blood indicated early bioaccumulation effects, which declined during contour feather production, and subsequently increased when feather production ceased. These results indicate that prefledge osprey are at highest risk of long-term neurological damage between hatching and the two weeks of feeding before contour feathers appear. Furthermore, a negative correlation between blood mercury in lake nestlings between 1051 g to 1400 g (about six weeks old, when the birds mercury excretion by molting feathers ceases) and fledgling production. Osprey nestlings from 64% of lake nests carried Hg burdens above levels of concern found in the scientific literature (blood max 0.81 ppm, feather max 13.5 ppm). Mercury exposure and bioaccumulation was more of a threat to the osprey being reared on the shallow lake habitat than open estuarine environment. |