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Raptors, including eagles, are geographically widespread and sit atop the food chain, thereby serving an important role in maintaining ecosystem balance. After facing population declines associated with exposure to organochlorine insecticides such as dichlorodiphenyltrichloroethane (DDT), bald eagles ( Haliaeetus leucocephalus ) have recovered from the brink of extinction. However, both bald and golden eagles ( Aquila chrysaetos ) are exposed to a variety of other toxic compounds in the environment that could have population impacts. Few studies have focused on anticoagulant rodenticide (AR) exposure in eagles. Therefore, the purpose of this study was to determine the types of ARs that eagles are exposed to in the USA and better define the extent of toxicosis (i.e., fatal illness due to compound exposure). Diagnostic case records from bald and golden eagles submitted to the Southeastern Cooperative Wildlife Disease Study (University of Georgia) 2014 through 2018 were reviewed. Overall, 303 eagles were examined, and the livers from 116 bald eagles and 17 golden eagles were tested for ARs. The percentage of AR exposure (i.e., detectable levels but not associated with mortality) in eagles was high; ARs were detected in 109 (82%) eagles, including 96 (83%) bald eagles and 13 (77%) golden eagles. Anticoagulant rodenticide toxicosis was determined to be the cause of mortality in 12 (4%) of the 303 eagles examined, including 11 bald eagles and 1 golden eagle. Six different AR compounds were detected in these eagles, with brodifacoum and bromadiolone most frequently detected (81% and 25% of eagles tested, respectively). These results suggest that some ARs, most notably brodifacoum, are widespread in the environment and are commonly consumed by eagles. This highlights the need for research to understand the pathways of AR exposure in eagles, which may help inform policy and regulatory actions to mitigate AR exposure risk.

The cyclic GMP-AMP synthase (cGAS) catalyzes the synthesis of the multifunctional second messenger, cGAMP, in metazoans. Although numerous cGAS homologues are predicted in protein databases, the catalytic activity towards cGAMP synthesis has been proven for only four of them. Therefore, we selected five novel and yet uncharacterized cGAS homologues, which cover a broad range in the field of vertebrates. Cell-free protein synthesis (CFPS) was used for a pre-screening to investigate if the cGAS genes originating from higher organisms can be efficiently expressed in a bacterial expression system. As all tested cGAS variants were expressible, enzymes were synthesized in vivo to supply higher amounts for a subsequent in vitro activity assay. The assays were carried out with purified enzymes and revealed vast differences in the activity of the homologues. For the first time, the cGAS homologues from the Przewalski’s horse, naked mole-rat, bald eagle, and zebrafish were proven to catalyze the synthesis of cGAMP. The extension of the list of described cGAS variants enables the acquisition of further knowledge about the structural and molecular mechanism of cGAS, potentially leading to functional improvement of the enzyme.

Trophic transfer of perfluorooctanesulfonate (PFOS) and other related perfluorinated compounds was examined in a Great Lakes benthic foodweb including water-algae-zebra mussel-round goby-smallmouth bass. In addition, perfluorinated compounds were measured in livers and eggs of Chinook salmon and lake whitefish, in muscle tissue of carp, and in eggs of brown trout collected from Michigan. Similarly, green frog livers, snapping turtle plasma, mink livers, and bald eagle tissues were analyzed to determine concentrations in higher trophic-level organisms in the food chain. PFOS was the most widely detected compound in benthic organisms at various trophic levels. Concentrations of PFOS in benthic invertebrates such as amphipods and zebra mussels were approximately 1000-fold greater than those in surrounding water, which suggested a bioconcentration factor (BCF; concentration in biota/concentration in water) of 1000 in benthic invertebrates. Concentrations of PFOS in round gobies were two- to fourfold greater than those in their prey organisms such as zebra mussels and amphipods. Concentrations of PFOS in predatory fishes (Chinook salmon and lake whitefish) were 10 to 20-fold greater than those in their prey species. Concentrations of PFOS in mink and bald eagles were, on average, 5- to 10-fold greater than those in Chinook salmon, carp, or snapping turtles. Because of the accumulation of PFOS in liver and blood, the biomagnification factor (BMF) of perfluorinated compounds in higher trophic-level organisms such as salmonid fishes, mink, and eagles were based on the concentrations in livers or plasma. Overall, these results suggest a BCF of PFOS of approximately 1000 (whole-body based) in benthic invertebrates, and a BMF of 10 to 20 in mink or bald eagles, relative to their prey items. Eggs of fish contained notable concentrations of PFOS, suggesting oviparous transfer of this compound. PFOA was found in water, but its biomagnification potential was lower than that of PFOS.

Fish-eating birds can be exposed to levels of dietary methylmercury (MeHg) known or suspected to adversely affect normal behavior and reproduction, but little is known regarding Hg's subtle effects on the avian brain. In the current study, we explored relationships among Hg, Se, and neurochemical receptors and enzymes in two fish-eating birds--common loons (Gavia immer) and bald eagles (Haliaeetus leucocephalus). In liver, both species demonstrated a wide range of total Hg (THg) concentrations, substantial demethylation of MeHg, and a co-accumulation of Hg and Se. In liver, there were molar excesses of Se over Hg up to about 50-60 μg/g THg, above which there was an approximate 1:1 molar ratio of Hg:Se in both species. However, in brain, bald eagles displayed a greater apparent ability to demethylate MeHg than common loons. There were molar excesses of Se over Hg in brains of bald eagles across the full range of THg concentrations, whereas common loons often had extreme molar excesses of Hg in their brains, with a higher proportion of THg remaining as MeHg compared with eagles. There were significant positive correlations between brain THg and muscarinic cholinergic receptor concentrations in both species studied; whereas significant negative correlations were observed between N-methyl-D-aspartic acid (NMDA) receptor levels and brain Hg concentration. There were no significant correlations between brain Se and neurochemical receptors or enzymes (cholinesterase and monoamine oxidase) in either species. Our findings suggest that there are significant differences between common loons and bald eagles with respect to cerebral metabolism and toxicodynamics of MeHg and Se. These interspecies differences may influence relative susceptibility to MeHg toxicity; however, neurochemical responses to Hg in both species were similar.

Recreational ground squirrel shooting is a popular activity throughout the western United States and serves as a tool for managing ground squirrel populations in agricultural regions. Belding's ground squirrels (Spermophilus beldingi) are routinely shot in California, Nevada, and Oregon across habitats that overlap with breeding avian scavengers. Ground squirrels shot with lead (Pb)-based bullets may pose a risk to avian scavengers if they consume carcasses containing Pb fragments. To assess the potential risk to breeding avian scavengers we developed a model to estimate the number, mass, and distribution of Pb fragments in shot ground squirrels using radiographic images. Eighty percent of shot carcasses contained detectible Pb fragments with an average of 38.6 mg of Pb fragments. Seven percent of all carcasses contained Pb fragment masses exceeding a lethal dose for a model raptor nestling (e.g. American kestrel Falco sparverius). Bullet type did not influence the number of fragments in shot ground squirrels, but did influence the mass of fragments retained. Belding's ground squirrels shot with .17 Super Mag and unknown ammunition types contained over 28 and 17 times more mass of Pb fragments than those shot with .22 solid and .22 hollow point bullets, respectively. Ground squirrel body mass was positively correlated with both the number and mass of Pb fragments in carcasses, increasing on average by 76% and 56% respectively across the range of carcass masses. Although the mass of Pb retained in ground squirrel carcasses was small relative to the original bullet mass, avian scavenger nestlings that frequently consume shot ground squirrels may be at risk for Pb-induced effects (e.g., physiology, growth, or survival). Using modeling efforts we found that if nestling golden eagles (Aquila chrysaetos), red-tailed hawks (Buteo jamaicensis), and Swainson's hawks (B. swainsoni) consumed shot ground squirrels proportionately to the nestling's mass, energy needs, and diet, 100% of the nestling period would exceed a 50% reduction in delta-aminolevulinic acid dehydratase production threshold, the last 13-27% of the nestling stage would exceed a reduced growth rate threshold, but no nestlings would be expected to exceed a level of Pb ingestion that would be lethal.

Lead exposure from ingestion of bullet fragments is a serious environmental hazard to eagles. We determined blood lead levels (BLL) in 178 golden eagles ( Aquila chrysaetos ) captured during fall migration along a major North American flyway. These eagles spent the breeding season distributed over a large range and are the best currently available representation of free flying golden eagles on the continent. We found 58 % of these eagles containing increased BLL > 0.1 mg/L; 10 % were clinically lead poisoned with BLL > 0.6 mg/L; and 4 % were lethally exposed with BLL > 1.2 mg/L. No statistical difference in BLL existed between golden and bald eagles ( Haliaeetus leucocephalu s). Golden eagles captured on carrion had higher BLL than those captured using live bait suggesting differences in feeding habits among individuals. Median BLL increased with age class. We propose a conceptual model for the long-term increase in BLL after ingestion of lead particles. The mean blood mercury level in golden eagles was 0.023 mg/L. We evaluate a field test for BLL that is based on anodic stripping voltammetry. This cost-effective and immediate method correlated well with results from inductively coupled plasma–mass spectrometry, although results needed to be corrected for each calibration of the test kit.

This paper summarizes results from the monitoring of reproduction of white-tailed sea eagle in Sweden 1965–2006. Since 1989 the eagle population on the Swedish Baltic coast has been included in the National Environment Monitoring Program as an indicator species for potentially harmful chemicals. The percentage of successfully reproducing pairs and nestling brood size decreased in synchrony with rising concentrations of contaminants in the 1950s on into the 1970s. Mean productivity was 1.3 young per pair prior to 1950 and decreased to 0.3 in 1965–1985. Dichlorodiphenyldichloroethene (DDE) in eagle eggs decreased from a range of annual means in 1965–1974 of 600-1200 μg g−1 (lipid weight) to 60–140 μg g−1 in 1996–2005. Total polychlorinated biphenyl (PCB) concentrations averaged above 1000 μg g−1 into the early 1980s and remained in the range of 250–500 μg g−1 in 1996–2005. Productivity began to improve when concentrations of DDE and PCBs dropped below approximately 300 and 800 μg g−1, respectively. Brood size remains below the pre-1950 level in one coastal region, indicating a possible impact from other contaminants. The power to detect significant trends under the program is presented and discussed: if white-tailed sea eagle reproduction had been monitored earlier during the 20th century, the negative impact of dichlorodiphenyltrichloroethane (DDT, source of DDE) would have been signaled as early as the 1950s in the Baltic Sea. The dramatic fall of white-tailed sea eagle reproduction under the influence of DDT and PCBs, and the subsequent rise following their ban, illustrates the usefulness of raptors like sea eagles as sentinels for environmental pollutants.

The Spanish imperial eagle ( Aquila adalberti ) is found only in the Iberian Peninsula and is considered one of the most threatened birds of prey in Europe. Here we analyze lead concentrations in bones (n = 84), livers (n = 15), primary feathers (n = 69), secondary feathers (n = 71) and blood feathers (n = 14) of 85 individuals collected between 1997 and 2008 in central Spain. Three birds (3.6%) had bone lead concentration > 20 μg/g and all livers were within background lead concentration. Bone lead concentrations increased with the age of the birds and were correlated with lead concentration in rachis of secondary feathers. Spatial aggregation of elevated bone lead concentration was found in some areas of Montes de Toledo. Lead concentrations in feathers were positively associated with the density of large game animals in the area where birds were found dead or injured. Discontinuous lead exposure in eagles was evidenced by differences in lead concentration in longitudinal portions of the rachis of feathers.

Several polybrominated biphenyl ether (PBDE) congeners were found in all 175 osprey ( Pandion haliaetus ) eggs collected from the Columbia River Basin between 2002 and 2009. ΣPBDE concentrations in 2008–2009 were highest in osprey eggs from the two lowest flow rivers studied; however, each river flowed through relatively large and populous metropolitan areas (Boise, Idaho and Spokane, Washington). We used the volume of Wastewater Treatment Plant (WWTP) discharge, a known source of PBDEs, as a measure of human activity at a location, and combined with river flow (both converted to millions of gallons/day) created a novel approach (an approximate Dilution Index) to relate waterborne contaminants to levels of these contaminants that reach avian eggs. This approach provided a useful understanding of the spatial osprey egg concentration patterns observed. Individual osprey egg concentrations along the Upper Willamette River co-varied with the Dilution Index, while combined egg data (geometric means) from rivers or segments of rivers showed a strong, significant relationship to the Dilution Index with one exception, the Boise River. There, we believe osprey egg concentrations were lower than expected because Boise River ospreys foraged perhaps 50–75% of the time off the river at ponds and lakes stocked with fish that contained relatively low ΣPBDE concentrations. Our limited temporal data at specific localities (2004–2009) suggests that ΣPBDE concentrations in osprey eggs peaked between 2005 and 2007, and then decreased, perhaps in response to penta- and octa-PBDE technical mixtures no longer being used in the USA after 2004. Empirical estimates of biomagnification factors (BMFs) from fish to osprey eggs were 3.76–7.52 on a wet weight (ww) basis or 4.37–11.0 lipid weight. Our earlier osprey study suggested that ΣPBDE egg concentrations >1,000 ng/g ww may reduce osprey reproductive success. Only two of the study areas sampled in 2008–2009 contained individual eggs with ΣPBDE concentrations >1,000 ng/g, and non-significant ( P  > 0.30) negative relationships were found between ΣPBDEs and reproductive success. Additional monitoring is required to confirm not only the apparent decline in PBDE concentrations in osprey eggs that occurred during this study, but also to better understand the relationship between PBDEs in eggs and reproductive success.

In this study, osprey ( Pandion haliaetus ) tissues collected in France were used for contaminants analyses by a non-invasive approach. 53 pesticides (organochlorine, organophosphate, carbamate, pyrethroids, herbicides, anticoagulant rodenticides), 13 PCBs, and 5 metals (mercury, lead, cadmium, copper and arsenic) were quantified in liver of 14 individual samples. PCBs and mercury were frequent (mean 0.5 mg/kg, range < d.l.−2.6 mg/kg and mean 3.4 mg/kg, range < d.l.−16.3 mg/kg wet weight, respectively). Inter-individual variations in contaminant diversity and amounts were noticed. Immediate conservation of the species in the country does not seem to be threatened by global contamination.