Although THg concentrations in eggs produced by females collected from the contaminated portion of the South River exceed those associated with severe reproductive impairment observed in other amniotes (birds) exposure to Hg does not appear to be as consequential to turtle reproduction as it is in birds. For example, several studies have shown greater reductions in avian egg viability at lower egg Hg concentrations than were observed in turtle eggs sampled for the present study. Jackson et al. reported a 50% reduction in nest success of Carolina wrens (Thryothorus ludovicianus) when egg THg
concentrations reached ∼2.15 ppm (dwt). In free-living common loons, egg THg concentrations ranging from 2.7 to
3.6 ppm (dwt) were associated with a 28−48% decrease in hatchability mediated through embryotoxicity. In comparison,
C. serpentina collected from the same area contaminated with Hg produced eggs with average THg concentrations of 3.00 ± 0.183 ppm (dwt), which was associated with a 12% reduction in hatching success compared to the average hatching success at reference sites. From the regression equation generated from the observed egg Hg concentrations, turtles with egg Hg concentrations toward the upper end of the observed distribution (∼5.0 ppm, dwt) are predicted to have a 27%
reduction in hatching success. Together these comparisons indicate that turtle THg egg concentrations reported here
exceeded those reported in Jackson et al. and Barr but were associated with a less severe effect on embryonic survival, suggesting that sensitivity to egg Hg concentrations can vary considerably among taxa. This is similar to a previous study that reported interspecies variation in embryonic survival among several bird species dosed with the same concentration of Hg. Our findings suggest that C. serpentina may be more resilient to the adverse developmental effects of Hg than other amniotes, and perhaps better suited for long-term monitoring of bioavailability and bioaccumulation of Hg than as sensitive indicators of adverse effects. However, studies are needed to determine whether maternal transfer of Hg has latent or longterm effects that influence early survival of turtle hatchlings similar to those observed for other bioaccumulative contaminants