Mercury Exposure in Birds of Prey from Norway: Relation to Stable Carbon and Nitrogen Isotope Signatures in Body Feathers

Abstract

Mercury (Hg) and stable carbon and nitrogen isotope ratios were analysed in body feathers from nestlings of white-tailed eagles (Haliaeetus albicilla) (WTE; n = 13) and Northern goshawks (Accipiter gentilis) (NG; n = 8) and in red blood cells (RBC) from NG (n = 11) from Norway. According to linear mixed model, species factor was significant in explaining the Hg concentration in feathers (LMM; p < 0.001, estimate (WTE) = 2.51, 95% CI = 1.26, 3.76), with concentrations higher in WTE (3.01 ± 1.34 µg g−1 dry weight) than in NG (0.51 ± 0.34 µg g−1 dry weight). This difference and the isotopic patterns for each species, likely reflect their diet, as WTE predominantly feed on a marine and higher trophic-chain diet compared to the terrestrial NG. In addition, Hg concentrations in RBCs of NG nestlings were positively correlated with feather Hg concentrations (Rho = 0.77, p = 0.03), supporting the potential usefulness of nestling body feathers to biomonitor and estimate Hg exposure. Hg levels in both species were generally below the commonly applied toxicity threshold of 5 µg g−1 in feathers, although exceeded in two WTE (6.08 and 5.19 µg g−1 dry weight).

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

“…Piscivorous raptors, namely osprey and Haliaeetus eagles, are well-suited for Hg biomonitoring within and across multiple habitat types (marine, estuarine, river, lake) (Jackson et al 2016 ; Rumbold et al 2017 ; DeSorbo et al 2018 ; Sun et al 2019 ). Haliaeetus eagles are key sentinels in environmental programs used to monitor spatial and temporal Hg exposure patterns in North America, particularly in the U.S. Great Lakes ecosystem (Bowerman et al 2002 ) and in Fennoscandia (Sun et al 2019 ; Gómez-Ramírez et al 2023 ). A study of bald eagles ( Haliaeetus leucocephalus ) in the Great Lakes of the United States found evidence that Hg adversely affects a proportion of this population (Rutkiewicz et al 2011 ); in that study, 14–27% of individuals sampled were exposed to Hg at concentrations associated with subclinical neurological damage.…”