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

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.

Incorporation of Deepwater Horizon oil in a terrestrial bird

“…Adults and juveniles both feed on a variety of prey, including terrestrial as well as marine invertebrates (Post and Greenlaw 2006), thus exposing this species to a variety of contaminants through a number of potential routes. Consistent with this, the seaside sparrow was found to be a sensitive indicator species for mercury contamination in salt marshes (Warner et al 2010, Winder 2012.…”

Toxicity reference values for methylmercury effects on avian reproduction: Critical review and analysis

“…The resulting dose–response equation was extrapolated to Hg concentrations in eggs, based on a blood–egg regression equation . Several researchers have adopted the EC10 estimates from this dose–response analysis as a means of interpreting both egg and blood Hg concentrations in a variety of bird species .…”

Geographic Variation of Mercury in Breeding Tidal Marsh Sparrows of the Northeastern United States

“…Previous research suggests that up to 62% of saltmarsh sparrows breeding from Maine to New York, as well as >75% of saltmarsh sparrows and >60% of seaside sparrows wintering in North Carolina, are potentially at risk of deleterious MeHg effects on reproduction (Winder 2012;Lane et al 2020). A severe limitation in producing precise at-risk population estimates is the lack of toxicity reference values for our focal species.…”

“…A severe limitation in producing precise at-risk population estimates is the lack of toxicity reference values for our focal species. A common practice in ecotoxicological wildlife monitoring is to extrapolate toxicity reference values across species because many species have not been studied (Warner et al 2010;Lane et al 2011Lane et al , 2020Winder 2012).…”

“…Tidal marsh sparrows can be effective bioindicators for MeHg contamination of saltmarsh systems, and for quantifying the potential threat that MeHg poses to marsh bird populations, at a variety of geographic scales (Shriver et al 2006;Warner et al 2010;Lane et al 2011Lane et al , 2020Winder 2012;Ruskin et al In prep.). In all prior research, tidal marsh sparrow blood Hg levels have approached or exceeded 0.7 µg/g wet weight (Shriver et al 2006;Lane et al 2011Lane et al , 2020Warner et al 2010;Winder 2012;Ruskin et al In prep. ), a level that has been shown to influence nesting success in Carolina Wren ( Thryothorus ludovicianus ) (Jackson et al 2011).…”