Methylmercury is an environmental contaminant that bioaccumulates, and has multiple toxic modes of action. Aquatic species have traditionally been the focus of wildlife toxicological research on mercury, but terrestrial receptors, including passerines, may also be exposed to similarly elevated levels of methylmercury. In this study we exposed a model passerine, the Zebra Finch (Taeniopygia guttata), to methylmercury in-ovo (embryonic exposure, pre-hatching), only as a chick (post-hatching exposure), and with a combined in-ovo chick treatment (embryonic and post-hatching exposure). Exposure to methylmercury in-ovo resulted in a significant reduction in hatching success, but there was no significant difference in behavioural or reproductive outcomes for the individuals that survived to maturity. Birds dosed both in-ovo and as chicks had reduced numbers of females surviving to maturity and altered male courtship behaviours. Birds dosed only as chicks had reduced survival rates. No long-term effects were seen on male courtship in the birds dosed only as chicks. Continuous exposure of chicks during embryogenesis and chick development had a deleterious effect on bird survival and fertility. Passerines may be able to withstand exposure to elevated levels of methylmercury during development at the nestling stage, but chronic exposure may reduce survival and fertility.
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