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.Keywords: Songbird, Sentinel, Bioaccumulation, Mercury, Passeriforme