Session V: Bird Studies

Abstract #: 97504

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EFFECTS OF CHRONIC, LOW CONCENTRATIONS OF DIETARY METHYLMERCURY ON APPETITE AND HUNTING BEHAVIOR OF JUVENILE GREAT EGRETS
Shannon N. Bouton, Peter Frederick, Marilyn Spalding and Heather Lynch
Dept. Wildlife Ecology and Conservation, University of Florida, Gainesville, Florida 32611-0430

ABSTRACT
Wading birds (Ciconiiformes) in the Everglades are known to chronically encounter methylmercury in their diets. Based on concentrations of mercury in prey animals and measurements of food intake in wild nestlings, we estimate that Great Egrets typically encounter a minimum of 0.65 ppm in their diet. We dosed 6 captive juvenile Great Egrets with 0.5 ppm methylmercury, and 6 with placebos in their diets between 12 and 105 days of age in order to estimate the effects of this toxin during the critical growth and independence period. We tested each bird repeatedly for their ability to capture live fish in pools with contrasting and camouflage backgrounds. Placebo birds were significantly more likely to finish foraging bouts (5 fish presented sequentially) than were mercury-dosed birds. For birds which completed foraging bouts, there was no difference in time to capture fish.