Effects of chronic, low concentrations of dietary methylmercury on the behavior of juvenile great egrets

Abstract

Abstract We measured the behavioral effects of methylmercury on 16 great egret chicks (Ardea albus) in a captive dosing experiment. Birds were randomly divided into a control group and groups that received 0.5 or 5 mg methylmercury chloride per kilogram of food at between 12 and 105 d of age. We recorded activity levels, maintenance behavior, and foraging efficiency and determined that mercury affected activity and maintenance behavior. Birds dosed with 5 mg/kg became severely ataxic and were euthanized by 12 weeks of age. We found that, during the postfledging period, there were no differences between low-dose and placebo birds in time required to capture live fish in pools or in efficiency of capture. We did find that low-dose birds were less likely to hunt fish. Our results suggest that, at the 0.5 mg/kg concentration in food, there are significant effects of methylmercury on activity, tendency to seek shade, and motivation to hunt prey.