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Influence of in ovo mercury exposure, lake acidity, and other factors on common loon egg and chick quality in Wisconsin

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We conducted a field study in Wisconsin to characterize in ovo mercury (Hg) exposure in common loons (Gavia immer). Total Hg mass fractions ranged from 0.17 to 1.23 µg/g wet weight (ww) in eggs collected from nests on lakes representing a wide range of pH (5.0 ‐ 8.1) and were modeled as a function of maternal loon Hg exposure and egg laying order. Blood total Hg mass fractions in a sample of loon chicks ranged from 0.84 to 3.86 µg/g ww at hatch. Factors, other than mercury exposure, that may have persistent consequences on development of chicks from eggs collected on low pH lakes (i.e., egg selenium, calcium, and fatty acid mass fractions) do not seem to be contributing to reported differences in loon chick quality as a function of lake pH. However, we observed that adult male loons holding territories on neutral‐pH lakes were larger on average than those occupying territories on low‐pH lakes. Differences in adult body size of common loons holding territories on neutral‐ versus low‐pH lakes may have genetic implications for differences in lake‐source‐related quality (i.e., size) in chicks. The tendency for high in ovo Hg exposure and smaller adult male size to co‐occur in low pH lakes complicates the interpretation of the relative contributions of each to resulting chick quality. This article is protected by copyright. All rights reserved

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