John Wiley & Sons, Ltd.

Effect of laying sequence on egg mercury in captive zebra finches: An interpretation considering individual variation

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Bird eggs are widely used as noninvasive bioindicators for environmental mercury availability. However, previous studies have found varying relationships between laying sequence and egg mercury concentrations. Some studies have reported that the mercury concentration is higher in first‐laid eggs or declines across the laying sequence, whereas in other studies mercury concentration was not related to egg order. Approximately 300 eggs (61 clutches) were collected from captive zebra finches dosed throughout their reproductive lives with methylmercury (0.3, 0.6, 1.2 or 2.4 μg/g wet weight in diet); the total mercury concentration (mean ± SD dry weight basis) of their eggs was 7.03 ± 1.38 μg/g, 14.15 ± 2.52 μg/g, 26.85 ± 5.85 μg/g and 49.76 ± 10.37 μg/g, respectively (equivalent to fresh weight egg mercury concentrations of 1.24, 2.50, 4.74, and 8.79 μg/g). There was a significant decrease in the mercury concentration of successive eggs when compared with the first egg, and notable variation between clutches within treatments. The mercury level of individual females within and among treatments did not alter this relationship. Based on our results, sampling of a single egg in each clutch from anywhere in the laying sequence is sufficient for purposes of population risk assessment, but it is not recommended as a proxy for individual female exposure or as an estimate of average mercury level within the clutch. This article is protected by copyright. All rights reserved

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