A diet containing 3 ppm mercury was fed to black ducks (Anas rubripes) for periods of 28 weeks during two consecutive breeding seasons. Clutch size, egg production, number of eggs incubated, hatchability and survival of ducklings were lower during both years in hens fed mercury. Reduced hatchability and poor duckling survival were the most harmful effects. During 2 years, 13 pairs of breeders fed mercury produced only 16 ducklings that survived 1 week compared with 73 ducklings from 13 pairs of controls. Mercury residues in eggs, embryos and ducklings averaged about 30% lower during the second breeding season compared with first year results. Third eggs laid by treated hens contained a mean of 6?14 and 3?86 ppm mercury during the first and second years. Whole embryos that failed to hatch contained means of 9?62 and 6?08 ppm mercury during the first and second years. Brains of dead ducklings contained between 3?25 and 6?98 ppm mercury and exhibited lesions characteristic of mercury poisoning. Relative tissue mercury levels for treated adult breeders were: feathers > liver > kidney > breast muscle > brain. Mercury levels in males and females did not differ.
