Standing in the woods along the South River, Kelly Hallinger held the microphone up to capture the cacophony of songs, one at a time: the urgent, effervescent voice of the house wren; the teakettle whistle of the Carolina wren; and the sharp, shrill notes of the song sparrow.
It was the summer after her freshman year at the College of William and Mary in Williamsburg, and Hallinger was working with her professor, ecologist Dan Cristol, to investigate the effects of mercury left behind by a factory. Over and over she recorded birdsong, visiting various sites in the woods and along the shore, some polluted, some unpolluted.
When she got back to Williamsburg with her tape recorder, Hallinger sorted through the hours of bird songs. She turned them into digital files in the computer, then analyzed them. The differences were striking: The wrens and sparrows along the contaminated South River were singing simpler, shorter, lower-pitched songs.
Scientists have long known that mercury is a potent toxicant: It disrupts the architecture of human brains, and it can change birds’ behavior and kill their chicks. But after extensive research in rural Virginia, scientists have shown that mercury also alters the very thing that many backyard birds are known for-their songs.
Emitted by the burning of coal, mercury in the atmosphere has quadrupled since the days before industrialization, according to a recent study published in Nature. And the amount of methylmercury in animals throughout much of the world is rising, too.
“There’s a global decline in songbird populations,” and while the causes are unexplained, “I can’t help but think that mercury and other chemicals and organic compounds are partly implicated in this,” said Nil Basu, an environmental toxicologist at McGill University in Montreal.