Characterization of Mercury and Its Risk in Nelson’s, Saltmarsh, and Seaside Sparrows

Virginia L Winder,Kimberly Patraw Van Niel

doi:10.1371/journal.pone.0044446

Abstract

BackgroundNelson’s, Saltmarsh, and Seaside Sparrows (Ammodramus nelsoni, A. caudacutus, and A. maritimus, respectively) depend on marsh and wetland habitats – ecosystems in which mercury (Hg) bioavailability is notoriously high. The purpose of the present study was to address the potential impact of Hg on these species using first primary and breast feathers as non-destructive biomonitoring tools.Methods and Principal FindingsFeathers were sampled from wintering sparrows in North Carolina salt marshes (2006–2010). Feather Hg data were used in three risk analysis components (1) Threshold Component – examined feather Hg with regard to published negative effects thresholds; (2) Hg Dynamics Component – examined Hg in sparrows captured multiple times; and (3) Capture Frequency and Survival Component – tested for links between Hg and return frequency and survival. Threshold Component analyses indicated that Hg concentrations in 42–77% of sampled individuals (breast feather n = 879; first primary feather n = 663) were within the range associated with decreased reproduction in other avian species. Hg Dynamics Component analyses demonstrated that Hg increased between first and second captures for Nelson’s (n = 9) and Seaside Sparrows (n = 23). Capture Frequency and Survival Component analyses detected a negative relationship between Hg and capture frequency in Nelson’s Sparrows (n = 315). However, MARK models detected no effect of Hg on apparent survival in any species.Conclusion and SignificanceThis study indicates that current Hg exposure places a considerable proportion of each population at risk. In particular, 52% of all sampled Saltmarsh Sparrows exhibited first primary feather Hg concentrations exceeding those associated with a >60% reduction in reproductive success in other species. This study reports evidence for net annual bioaccumulation, indicating an increased risk in older individuals. These data can be used to inform future population assessments and management for these species.

Highlights

Anthropogenic sources account for approximately two-thirds of all input of mercury (Hg) into the environment [1]
This study indicates that current Hg exposure places a considerable proportion of each population at risk
52% of all sampled Saltmarsh Sparrows exhibited first primary feather Hg concentrations exceeding those associated with a .60% reduction in reproductive success in other species

Summary

Introduction

Anthropogenic sources account for approximately two-thirds of all input of mercury (Hg) into the environment [1]. Salt marsh habitats in North America are threatened by anthropogenic impacts such as habitat degradation, sea level rise, and pollution [13] Each of these species is of conservation concern [14,15,16,17]. Previous studies have characterized Hg exposure throughout portions of the ranges of Nelson’s and Saltmarsh Sparrows, reporting higher than expected and geographically variable concentrations of Hg in their tissues [11,12,18,19,20]. Nelson’s, Saltmarsh, and Seaside Sparrows (Ammodramus nelsoni, A. caudacutus, and A. maritimus, respectively) depend on marsh and wetland habitats – ecosystems in which mercury (Hg) bioavailability is notoriously high.

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Conclusion