Report suggests songbirds, bats at risk of mercury poisoning

Posted Jan. 24, 2012, at 7:34 p.m.

Researchers examining the effects of mercury on wildlife found elevated levels of the neurotoxin in songbirds and bats from Maine to Virginia, prompting the study’s authors to call for more monitoring and stronger conservation measures.

Researchers with the BioDiversity Research Institute, based in Gorham, and The Nature Conservancy compiled blood tests from nearly 1,900 birds and 800 bats collected over the past decade in the mid-Atlantic and the Northeast.

The resulting report, “Hidden Risk: Mercury in Terrestrial Systems of the Northeast,” states that some species of birds and bats may be absorbing dangerously high levels of mercury from the insects they eat. Although the authors acknowledge more study is needed, they said the results suggest that the neurotoxin may be taking a toll on species previously overlooked by scientists.

Among the species with “high risk” to “very high risk” levels of mercury were saltmarsh sparrows, indigo buntings, rusty blackbirds and Nelson’s sparrows. Big brown bats — a species common throughout the Northeast — had the highest levels of mercury contamination.

“Mercury accumulation has many implications for the health and survival of wildlife species across habitats, not just those that live and feed in aquatic habitats,” David Evers, executive director and chief scientist at the BioDiversity Institute, said in a statement. “Our research has found that mercury concentrations in animals that live in terrestrial environments are significant enough to cause physiological and reproductive harm.”

After mercury is emitted into the air by coal-burning power plants and other sources, it eventually settles to the ground in precipitation or in a dry state. Once on the ground, it is converted to methylmercury, the more toxic and organic form that can be absorbed by plants and animals.

Methylmercury magnifies as it moves up the food chain, so that a loon or a human that eats fish contaminated with mercury will accumulate higher levels of the neurotoxin linked to developmental and reproductive problems. “Hidden Risk” suggests that bug-eating birds and bats face similar risks as they devour insects, spiders, snails and other invertebrates contaminated with mercury.

Songbirds living and feeding in bogs, estuaries and similar areas — such as the saltmarsh sparrow — had the highest mercury contamination levels because the wet-dry cycle can lead to additional mercury being released into the environment in its organic form. But the study also found elevated levels in the Bicknell’s thrush, a high-altitude bird. That is likely because higher altitude areas are prone to more precipitation and therefore more exposure to mercury in cloud water, the authors stated.

As for possible solutions to the issue, “Hidden Risk” recommends the adoption of a nationwide mercury monitoring program that includes songbirds and bats. Additionally, the authors cheered the U.S. Environmental Protection Agency’s recently announced rules requiring coal-fired power plants to substantially reduce mercury emissions.

Other recommendations included restricting logging near water bodies, controlling reservoir levels to avoid remobilizing sequestered mercury, and tracing unknown sources of mercury.

“Reducing this neurotoxin from the environment will benefit wildlife and people,” Tim Tear with The Nature Conservancy said in a statement.

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