Using data collected by thousands of volunteer citizen-scientists in the Birds in Forested Landscapes project, scientists at the Cornell Lab of Ornithology showed that the wood thrush is less likely to attempt to breed in regions that receive high levels of acid rain. The finding is reported in the current Proceedings of the National Academy of Sciences (PNAS Vol.99 No. 16) by Ralph S. Hames, a postdoctoral associate at the Cornell Lab of Ornithology who conducted the research with colleagues Kenneth V. Rosenberg, James D. Lowe, Sara E. Barker and Andr A. Dhondt.
Acid rain is the broad term used to describe several ways that a weak solution of inorganic acids, such as nitric and sulfuric acid, falls out of the atmosphere as rain, snow, mist and fog. Sulfur dioxide (SO2) and oxides of nitrogen (NOx) are the primary causes of acid rain. In the United States, about two-thirds of all SO2 and one-fourth of all NOx come from electric-power generation that relies on burning fossil fuels, such as coal.
High elevations, such as the Adirondack, Appalachian and Great Smokey mountains as well as the Allegheny Plateau, where the amount of acid deposited in precipitation could be highest, show long-term declines of up to nearly 5 percent annually in wood thrush populations. Although the exact mechanism leading to the declines is still unknown, it may well be related to the leaching of calcium from the soil by acid rain, according to Hames. European studies of heavy acid-rain regions similarly have linked declining bird populations to acid-rain-induced depletion of soil calcium.