U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, OR, 97331, USA.
U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, OR, 97331, USA.
Environ Pollut. 2018 Dec;243(Pt A):610-619. doi: 10.1016/j.envpol.2018.09.005. Epub 2018 Sep 5.
Mercury (Hg) and lead (Pb) are widespread contaminants that pose risks to avian scavengers. In fact, Pb exposure is the primary factor limiting population recovery in the endangered California condor (Gymnogyps californianus) and Hg can impair avian reproduction at environmentally relevant exposures. The Pacific Northwest region of the US was historically part of the condor's native range, and efforts are underway to expand recovery into this area. To identify potential threats to reintroduced condors we assessed foraging habitats, Hg and Pb exposure, and physiological responses in two surrogate avian scavenger species (common ravens [Corvus corax] and turkey vultures [Cathartes aura] across the region between 2012 and 2016. Mercury exposure near the Pacific coast was 17-27-fold higher than in inland areas, and stable carbon and sulfur isotopes ratios indicated that coastal scavengers were highly reliant on marine prey. In contrast, Pb concentrations were uniformly elevated across the region, with 18% of the birds exposed to subclinical poisoning levels. Elevated Pb concentrations were associated with lower delta-aminolevulinic acid dehydratase (δ-ALAD) activity, and in ravens there was an interactive effect between Hg and Pb on fecal corticosterone concentrations. This interaction indicated that the effects of Hg and Pb exposure on the stress axis are bidirectional, and depend on the magnitude of simultaneous exposure to the other contaminant. Our results suggest that condors released to the Pacific Northwest may be exposed to both elevated Hg and Pb, posing challenges to management of future condor populations in the Pacific Northwest. Developing a robust monitoring program for reintroduced condors and surrogate scavengers will help both better understand the drivers of exposure and predict the likelihood of impaired health. These findings provide a strong foundation for such an effort, providing resource managers with valuable information to help mitigate potential risks.
汞（Hg）和铅（Pb）是广泛存在的污染物，对食腐鸟类构成威胁。事实上，Pb 暴露是限制濒危加利福尼亚秃鹫（Gymnogyps californianus）种群恢复的主要因素，而 Hg 可以在环境相关暴露水平下损害鸟类繁殖。美国太平洋西北地区曾是秃鹫的原生栖息地，目前正在努力将其恢复范围扩大到该地区。为了确定重新引入的秃鹫可能面临的威胁，我们评估了 2012 年至 2016 年期间该地区两种替代食腐鸟类（普通乌鸦[Corvus corax]和土耳其秃鹰[Cathartes aura]）的觅食栖息地、Hg 和 Pb 暴露情况以及生理反应。太平洋沿岸的 Hg 暴露量比内陆地区高 17-27 倍，稳定的碳和硫同位素比值表明，沿海食腐动物高度依赖海洋猎物。相比之下，Pb 浓度在整个地区都普遍升高，有 18%的鸟类暴露在亚临床中毒水平。Pb 浓度升高与 δ-氨基酮戊酸脱水酶（δ-ALAD）活性降低有关，而在乌鸦中，Hg 和 Pb 对粪便皮质酮浓度有交互作用。这种相互作用表明，Hg 和 Pb 暴露对应激轴的影响是双向的，并且取决于同时暴露于另一种污染物的程度。我们的研究结果表明，释放到太平洋西北地区的秃鹫可能会同时暴露于高浓度的 Hg 和 Pb，这对管理未来太平洋西北地区的秃鹫种群构成挑战。为重新引入的秃鹫和替代食腐动物制定一个强大的监测计划，将有助于更好地了解暴露的驱动因素，并预测健康受损的可能性。这些发现为这一努力提供了坚实的基础，为资源管理者提供了有价值的信息，以帮助减轻潜在风险。
