Relationships among Mercury Concentrations, Hormones, and Nesting Effort of White Ibises (eudocimus Albus) in the Florida Everglades

tions through acute toxicity or through physiological eff ects that modify behavior and negatively infl uence reproductive success. We compared body-feather mercury concentrations of free-living male and female adult White Ibises (Eudocimus albus) during three breeding seasons in the Florida Everglades and examined the relationships among mercury, hormone concentrations, and body-condition scores. Female White Ibises consistently had lower mercury concentrations than males. Prebreeding females’ estradiol concentrations were negatively correlated with mercury concentrations. However, we found no relationship between mercury and female testosterone, progesterone, and corticosterone concentrations. Incubating male White Ibises showed a signifi cant positive relationship between testosterone and mercury concentrations, but no other signifi cant hormonal correlations with mercury concentrations. We used a seven-year standardized data set of Great Egret (Ardea alba) chick-feather mercury concentrations as a measure of temporal changes in mercury bioavailability in the Everglades and related that measure to annual numbers of White Ibis nests. White Ibis nesting was negatively correlated with the mercury exposure index. Low numbers of nesting White Ibises may have been the result of fewer birds nesting or high abandonment rates. Our results suggest that mercury exposure may cause fewer birds to nest or more birds to abandon nests because of subacute eff ects on hormone systems. However, the results are correlative; they call for further investigation in free-living populations and in the laboratory. Received 23 May 2003, accepted 23 September 2004.