Songbirds as sentinels of mercury in terrestrial habitats of eastern North America

Abstract

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.

Avian mercury exposure and toxicological risk across western North America: A synthesis

“…A few studies have synthesized the available data on bird mercury contamination within the Great Lakes and northeastern regions of the United States and Canada (Evers et al, 2011; Jackson et al, 2015) and the Canadian Arctic (Mallory and Braune, 2012), but no such studies exist elsewhere in North America. Western North America is characterized by a diverse gradient of habitats, including both extremely dry and wet regions (National Assessment Synthesis Team, 2001).…”

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

“…Extensive data have become available over the past decade to inform the development of Hg TRVs for avian risk assessment. In addition to new studies on aquatic-feeding species [10][11][12][13][14], songbirds have increasingly become a subject of investigation [15]. Another recent development is increasing reliance on blood Hg analyses as a primary tool for monitoring avian Hg exposures [13,14].…”

Isotopic study of mercury sources and transfer between a freshwater lake and adjacent forest food web

“…Previous studies of MMHg sources and biogeochemical pathways in aquatic ecosystems have been extensive, but studies in terrestrial ecosystems have been more limited. A number of recent studies have reported elevated MMHg levels in terrestrial organisms such as spiders Paetzold et al, 2011;Tweedy et al, 2013), birds Evers et al, 2008;Jackson et al, 2015) and bats (Evers et al, 2012;Wada et al, 2010) collected across North American forests. The MMHg concentrations in these organisms have been linked to reproductive failure, physiological alteration, and neurological deficit Evers et al, 2008).…”