Mercury in breeding saltmarsh sparrows (Ammodramus caudacutus caudacutus)

Abstract

Environmental mercury exposure of birds through atmospheric deposition and watershed point-source contamination is an issue of increasing concern globally. The saltmarsh sparrow (Ammodramus caudacutus) is of high conservation concern throughout its range and the potential threat of mercury exposure adds to other anthropogenic stressors, including sea level rise. To assess methylmercury exposure we sampled blood of the northern nominal subspecies of saltmarsh sparrows (A. c. caudacutus) nesting in 21 tidal marshes throughout most of the species' breeding range. Blood of tree swallows (Tachycineta bicolor) was sampled concurrently at three of these sites to provide a comparison with a well-studied songbird that is a model species in ecotoxicology. Arithmetic means (±1 SD) ranged from 0.24 ± 0.06 μg g(-1) wet weight (ww) in Connecticut to 1.80 ± 0.14 μg g(-1) ww in Massachusetts, differing significantly among sites. Comparison to tree swallows indicates that mercury exposure is significantly higher in saltmarsh sparrows, making them a more appropriate bioindicator for assessing risk to methylmercury toxicity in tidal marsh ecosystems.

Mercury in non-breeding sparrows of North Carolina salt marshes

“…From those well-supported models, we have detected factors that contribute to tissue Hg levels in Nelson's, Seaside and Saltmarsh Sparrows, and careful consideration of the time frame of Hg exposure represented in each tissue has allowed us to form hypotheses on how these factors may be interrelated in overall Hg dynamics. The dependence of Hg availability on temporally and spatially dynamic and interrelated factors leads to the potential for Hg to vary across space and time (Edmonds et al 2010;Lane et al 2011;Lane and Evers 2007). Therefore, it was not unexpected that parameters representing time and/or space should receive strong support in the most parsimonious models for each tissues we examined.…”

“…In part because salt marshes represent some of the most functionally degraded habitats in North America (Greenlaw and Woolfenden 2007), each of these species is of conservation concern (Dettmers and Rosenberg 2000;IUCN 2010;Rich et al 2004;USFWS 2002). Previous studies have characterized Hg exposure throughout portions of the ranges of Nelson's and Saltmarsh Sparrows, reporting higher than expected and geographically variable levels of Hg in the tissues of these omnivorous songbirds Lane et al 2011;Shriver et al 2006;Winder and Emslie 2011). For these reasons, and because of the environmental threats already identified for these species (DiQuinzio et al 2001;Greenlaw and Woolfenden 2007), further research is necessary to determine when, where and how Hg levels may pose an additional threat.…”

Mercury exposure affects the reproductive success of a free-living terrestrial songbird, the Carolina Wren (Thryothorus ludovicianus)

“…Methylmercury is the most bioavailable and toxic form of mercury (Wiener et al 2003); consequently, many studies investigating mercury exposure in birds have focused on fish-eating species that obtain their food from wetland or aquatic environments (Wolfe et al 2007, Scheuhammer et al 2007. Bioaccumulation of mercury also occurs in terrestrial habitats, however, and adverse effects of mercury exposure on nonpiscivorous species are increasingly apparent (Evers et al 2005, Edmonds et al 2010, Hallinger and Cristol 2011, Jackson et al 2011a, 2011b, Lane et al 2011.…”

Mercury in the Great Lakes region: bioaccumulation, spatiotemporal patterns, ecological risks, and policy

“…A single species of sparrow, the swamp sparrow (Melospiza georgiana), was examined in Wisconsin by Strom and Brady (2011). However, it is known that different-even closely related-species of songbirds often accumulate methylmercury at very different rates Evers et al 2011c;Lane et al 2011). The saltmarsh sparrow (Ammodramus caudacutus), for instance, appears to accumulate mercury much more efficiently than Nelson's sparrows (Ammodramus nelsoni) (Shriver et al 2006;Cristol et al 2011) or tree swallows (Lane et al 2011) foraging in the same location.…”

“…However, it is known that different-even closely related-species of songbirds often accumulate methylmercury at very different rates Evers et al 2011c;Lane et al 2011). The saltmarsh sparrow (Ammodramus caudacutus), for instance, appears to accumulate mercury much more efficiently than Nelson's sparrows (Ammodramus nelsoni) (Shriver et al 2006;Cristol et al 2011) or tree swallows (Lane et al 2011) foraging in the same location. Threshold concentrations for adverse effects appear to be lower in songbirds than in fish-eating birds, sometime by an order of magnitude (Heinz et al 2009).…”