Mercury in eggs and feathers of great egrets (Ardea albus) from the Florida everglades

Great egret (Ardea albus) eggs and nestling feathers were collected for tot al mercury (THg) and methylmercury (MeHg) analysis from two colonies in the Florida Everglades in 1999 and 2000. THg was present in all eggs at a mean concentration of 0.39 +/- 0.19 mug/g fresh weight (n = 33, range = 0.08-0. 86 mug/g). Egg-THg levels did not differ significantly between colonies or years. MeHg concentration in eggs was 0.35 +/- 0.18 mug/g fresh weight (n = 20, range = 0.05-0.82 mug/g,), and on average represented 85% of the THg f ound in the egg. Concentration of THg in feathers from egret nestlings, age 11-31 days, ranged from 1.4 to 8.6 mug/g dry weight. Feather-THg levels al so did not differ significantly between colonies or years. THg concentratio ns in feathers, normalized based on bill length, were positively correlated to THg concentrations in eggs from the same clutch. Levels of THg in both eggs and feathers were lower in 1999 and 2000 than values reported for simi lar samples collected in 1993-95, indicating that MeHg exposure has decreas ed in the southern Everglades since the mid-1990s. THg levels in eggs and n estling feathers for the period of this study were below levels associated with toxic reproductive effects. Clutch size, fledging success, and brood s ize observed in this study were consistent for this species in the Everglad es. Collectively, these results suggest that MeHg was not adversely affecti ng the reproductive performance of this population during the study.