Songbirds as sentinels of mercury in terrestrial habitats of eastern North America
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Mercury (Hg) is a globally distributed environmental contaminant with a variety of deleterious effects in fish, wildlife, and humans. Breeding songbirds may be useful sentinels for Hg across diverse habitats because they can be effectively sampled, have well-defined and small territories, and can integrate pollutant exposure over time and space. We analyzed blood total Hg concentrations from 8,446 individuals of 102 species of songbirds, sampled on their breeding territories across 161 sites in eastern North America [geometric mean Hg concentration = 0.25 μg/g wet weight (ww), range <0.01–14.60 μg/g ww]. Our records span an important time period—the decade leading up to implementation of the USEPA Mercury and Air Toxics Standards, which will reduce Hg emissions from coal-fired power plants by over 90 %. Mixed-effects modeling indicated that habitat, foraging guild, and age were important predictors of blood Hg concentrations across species and sites. Blood Hg concentrations in adult invertebrate-eating songbirds were consistently higher in wetland habitats (freshwater or estuarine) than upland forests. Generally, adults exhibited higher blood Hg concentrations than juveniles within each habitat type. We used model results to examine species-specific differences in blood Hg concentrations during this time period, identifying potential Hg sentinels in each region and habitat type. Our results present the most comprehensive assessment of blood Hg concentrations in eastern songbirds to date, and thereby provide a valuable framework for designing and evaluating risk assessment schemes using sentinel songbird species in the time after implementation of the new atmospheric Hg standards.
KeywordsBioaccumulation Mercury Passeriformes Sentinel Songbird
Funding and in kind support for this synthesis project came from a variety of sources including The Nature Conservancy (TNC) Rodney Johnson and Katherine Ordway Stewardship Endowment, New York State Energy Research and Development Authority (NYSERDA), U.S. Fish and Wildlife Service (USFWS), National Parks Service (NPS), and the Wildlife Conservation Society (WCS) and the U.S. Geological Survey. Special thanks to those people who helped secure funding, including Greg Lampman at NYSERDA, and Ken Karwowski, Ann Secord, Anne Condon and John Schmerfeld at USFWS. Many researchers contributed data or logistical support for this project, including: David Braun (Sound Science), Chris Rimmer and Kent McFarland (Vermont Center for Ecostudies), Greg Shriver (University of Delaware), Jeff Loukmas (New York State Department of Environmental Conservation), Chad Seewagen (WCS), Bill DeLuca, Bill Schuster (Black Rock Forest), Bob Mulvihill (Powdermill Avian Research Center), Mike Fowles (Army Corp of Engineers), Tom LeBlanc (Allegany State Park), Bruce Connery (Acadia National Park), Dr. Mark Ford (Fernow Experimental Forest), and Henry Caldwell (Dome Island). We are indebted to those that provided site access, including staff at Montezuma National Wildlife Refuge (NWR), Rachel Carson NWR, Wertheim NWR, Parker River NWR, Ninigret NWR, McKinney NWR, Great Meadows NWR, Maine Department of Inland Fisheries and Wildlife, Tonawanda Wildlife Management Area, Marine Nature Study Area and the town of Hempstead, NY, and everyone at the Cornell Lab of Ornithology. R.L. Brasso and A. Condon helped revise a previous draft of this manuscript.
Conflict of interest
The authors declare that they have no conflict of interest.
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