Mercury levels of Nelson’s and saltmarsh sparrows at wintering grounds in Virginia, USA
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Nelson’s and saltmarsh sparrows (Ammodramus nelsoni and A. caudacutus) have recently been recognized as separate species, and because of their limited distributions and the susceptibility of their wetland habitats to climate change, these two new species are of conservation concern. Both species are known to bioaccumulate mercury at breeding sites in New England, USA where their ranges overlap, with the saltmarsh sparrow reported to have twice the concentration of blood total mercury. In this study we sampled both species on their shared wintering grounds, and documented that mercury exposure is lower than that reported for the breeding range, with saltmarsh sparrow blood mercury 2.6 times higher than in Nelson’s sparrow. Feather mercury, which is incorporated on the breeding grounds, confirmed that saltmarsh sparrows had incorporated 2.3 times more mercury than Nelson’s sparrows during the previous breeding season. A comparison of stable isotopes of nitrogen and carbon suggests that the higher exposure of saltmarsh sparrows may be not due to feeding at a higher trophic level, as previously hypothesized, but rather could be related to a difference in the carbon source at the base of each species’ food chain. This study, along with recently published data from both species on additional breeding and wintering grounds, provides a more complete picture of relative mercury exposure. Saltmarsh sparrows are exposed to mercury levels that warrant concern, with the highest exposure being during the breeding season. Areas set aside for the long-term conservation of this species should be carefully assessed for mercury bioaccumulation.
KeywordsChesapeake Bay Mercury Nelson’s sparrow Saltmarsh sparrow Stable isotopes Wintering ground
We are indebted to James Junda, Sarah Bastarache, Mikaela Howie, Andrew Mcgann, Leah Gibala Smith, Kjarstin Carlson-Drexler, and the Eastern Shore Master Naturalists club for providing field and laboratory support. Susan Lingenfelser, Susan Rice, Joelle Buffa, Pam Denmon, John Gallegos, and Cyrus Brame provided logistical support. Financial support was provided by the William and Mary Undergraduate Science Education and Research Program sponsored by the Howard Hughes Medical Institute, USFWS Environmental Contaminants Division—Virginia Field Office, Gloucester, Virginia, and The Center for Conservation Biology at The College of William & Mary/Virginia Commonwealth University.
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