669. Song Birds and Bats Suffer from Mercury Poisoning

Wood Thrush suffers neurological disorder
caused by mercury poisoning

By Anthony De Palma, The New York Times, January 23, 2012

The strict new federal standards limiting pollution from power plants are meant to safeguard human health. But they should have an important side benefit, according to a study being released on Tuesday: protecting a broad array of wildlife that has been harmed by mercury emissions.

The little brown bat, which is already stressed by white-nose syndrome, is another species affected by mercury exposure.

Songbirds and bats suffer some of the same types of neurological disorders from mercury as humans and especially children do, says the study, “Hidden Risk,” by the Biodiversity Research Institute, a nonprofit organization in Gorham, Me., that investigates emerging environmental threats.

Methylmercury, the most toxic form of the heavy metal, was found to be widespread throughout the Northeast — not just in lakes and rivers, as had already been known, but also in forests, on mountaintops and in bogs and marshes that are home to birds long thought to be at minimal risk.

The new study found dangerously high levels of mercury in several Northeastern bird species, including rusty blackbirds, saltmarsh sparrows and wood thrushes. Previous studies have shown mercury’s effects on loons and other fish-eating waterfowl, as well as bald eagles, panthers and otters. In one study, zebra finches lost the ability to hit high notes in mating songs when mercury levels rose, affecting reproduction.

“We’re seeing many other species in a much larger landscape of harm from mercury,” said the principal author, David C. Evers, who is the institute’s executive director. He called the Environmental Protection Agency’s new mercury standards, adopted last month and scheduled to take effect over the next four years, “an excellent step forward in reducing and minimizing the impact on ecosystems and improving ecological health, and therefore our own health.”

Mercury, which occurs naturally in the earth, is released into the air when coal is burned in power plants. The gaseous mercury can drift hundreds of miles before settling back to earth, sometimes along with rain. The mercury can be absorbed by tree leaves; when they fall to the ground they are swarmed by bacteria and other organisms that convert the mercury to its organic form. The organic form, methylmercury, is a neurotoxin that can enter the food chain. Small insects, worms and snails that feed on forest litter absorb the mercury. In turn, they are eaten by birds and other small animals, and so on through the food chain.

Dr. Evers said levels of contamination were highest in habitats like marshes and beaver ponds that go through cycles of wet and dry, even if they are far from power plants. He also found that threshold levels at which some species begin to feel the effects of mercury are much lower than previously thought.

Songbirds with blood mercury levels of just 0.7 parts per million generally showed a 10 percent reduction in the rate at which eggs successfully hatched. As mercury increases, reproduction decreases. At mercury levels of greater than 1.7 parts per million, the ability of eggs to hatch is reduced by more than 30 percent, according to the study.

Over all, birds in contaminated sites were found to be three times as likely to abandon their nests or exhibit abnormal incubation or feeding behavior. In some nests, the chicks seemed to have been affected most; they vocalized less and did not beg as aggressively to be fed.

Such consequences mimic the effects of mercury on humans whose primary contact with the toxin is through the consumption of fish. The contamination can be passed to children in the womb or while they are nursing, damaging their nervous systems and impairing their ability to learn.

“It’s incredibly important that someone is following what is happening to these birds,” said Joanna Burger, a behavioral ecologist at Rutgers University who has studied mercury contamination in animals. “The birds not only act as sentinels to what is happening in nature, but the results of these studies propose hypotheses for effects that have not yet been identified for people.” 

Dr. Evers has been studying mercury in terrestrial species for 11 years across 11 states, from Virginia to Maine, continually adding new species and ecosystems. In the latest study, done in cooperation with the Nature Conservancy, biologists found that little brown bats, already stressed by white nose syndrome in the Northeast, accumulate substantial amounts of mercury because they can live up to 30 years — three times as long as songbirds.

The mercury is believed to cause bats to act erratically, and in some cases to lose their adeptness at avoiding wind turbine blades.

“What people don’t realize is that our rain isn’t just acidic,” said Timothy H. Tear, director of science for the Nature Conservancy in New York. “It is neurotoxic.”

The effects of mercury can lead to the degradation of entire ecosystems, Dr. Tear explained. “You don’t see birds falling off tree limbs because they have too much mercury,” he said, “but they’re not doing the job they used to.”