By Michelle Werts

For years now, there have been studies and concerns about mercury levels in our oceans and bodies of water and how they affect aquatic life and consequently those of us that rely on fish and shellfish for sustenance — from children to birds and fish-eating mammals. But these studies hadn’t really examined mercury’s affect on terrestrial invertivores, aka land-based insect eaters. Until now. And unsurprisingly, the news isn’t good.

Rusty blackbird
Rusty blackbird. Credit: Vlad Litvinov (vlitvinov)/Flickr

A new report released by the Biodiversity Research Institute last week reveals that many species of songbirds and bats in the Northeast are exhibiting high mercury levels that are leading to adverse effects on reproduction, among other things. How are birds and bats getting such high levels of mercury in their systems? It’s all about the cycle of life with a heap of emissions on top.

Industrial plants, especially coal-firing ones, release mercury emissions into the air. These emissions eventually settle onto our trees and plants and are absorbed or settle into the soil, where — under the right environmental factors, such as wet areas with the right bacteria — the mercury is transformed into methylmercury, its most toxic form. Then, invertebrates, aka insects, consume mercury or methylmercury-contaminated leaf matter. Spiders and other predatory insects eat these smaller insects, absorbing multiple sources of mercury. Birds eat the spiders. And the cycle perpetuates. Each level higher on the food chain has the potential to consume more mercury than the level before, and pretty soon, birds and bats find their systems full of mercury.

While the highest mercury levels have been detected in areas marked by strong wet-dry cycles, like bogs and marshes, the study also found elevated mercury blood levels in species living in deciduous and high-elevation forests. The study found that species such as the rusty blackbird, the saltmarsh sparrow and the little brown bat were experiencing dangerously high levels of mercury. The consequences include decreased reproduction success because it alters the animals’ neurochemistry, affecting timing, instincts and other precise requirements to breeding success. And the poor little brown bat: the mercury compromises its immune system at a time when it’s already facing a deadly bat-killer, white-nose fungus.

At least some hope is on the horizon, as the EPA finally created a set of regulations for mercury emissions last month, which will hopefully help curb mercury emissions and their fallout because as we’re quickly learning, it appears that it’s fallout is widespread.