12 - Mercury Exposure in Neotropical Birds: A Review and Prospectus

The monitoring of anthropogenic mercury (Hg) exposure to wildlife has been severely neglected throughout the Neotropics. This lack of prioritization has limited our capacity to assess the impacts of the ongoing degradation of primary forests via artisanal gold mining activities, the largest polluting sector of environmental Hg in the world, on Neotropical biodiversity. Due to their global abundance and relative ease of detection, capture, tracking, and identification compared to other taxa, birds stand apart as the most cost-effective organism for biodiversity and ecotoxicological monitoring in tropical, terrestrial systems. We summarize the largest dataset on Neotropical bird Hg concentrations: with over 1600 blood and feather samples from 285 species in 8 countries across Central America, South America, and the West Indies. Our findings align with those documented in temperate regions. There was high spatial variability in Hg exposure, and Hg concentrations tended to be highest in bird species that occupy higher trophic positions — such as piscivores and invertivores. We show the first evidence that artisanal and small-scale gold mining has a spatial influence on bird Hg exposure, which illustrates a rapid need to quantify potential toxic impacts to Neotropical avian communities. To make future Hg biomonitoring efforts more efficient and comparable, we created an inclusive and equitable data-sharing platform that unites an international network of tropical ornithologists. By standardizing sampling methods among contributing monitoring programs and prioritizing key polluting zones and sentinel species, the Tropical Research for Avian Conservation and Ecotoxicology (TRACE) Initiative seeks to better inform conservation decision making through the understanding of the prevalence, variation, persistence, and distribution of anthropogenic Hg in tropical biomes, and how this contaminant impacts both resident and migratory bird populations.