Mercury Poisoning Is Harming Songbirds

Wood Thrush / USFWS Photo

A new study by scientists at the Biodiversity Research Institute confirms that songbirds suffer harmful effects from ingesting methylmercury, one of the toxic chemicals produced by burning coal for energy. Despite some moves towards cleaner energy sources, coal is still the principal fuel for producing electricity through much of the Midwest and Northeast. The emissions from power plants include methylmercury in addition to carbon dioxide and other chemicals; the methylmercury is absorbed by tree leaves or falls to the ground in rainstorms and subsequently enters the food web.

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.”

And the results of mercury poisoning were quite severe, even at fairly low levels of contamination.

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.

The authors found similar effects in bats that they tested. Perhaps the new mercury regulations will reduce some of these problems over the next decade or two.