Acid Rain Study Introduction

A number of studies have demonstrated the relationship between acid rain, depletion of calcium in the soil, and the steep declines of many European bird species. This led BFL scientists to question the extent to which acid rain was linked to declines of bird species breeding in eastern North America, such as the Wood Thrush, which has suffered steep population declines over the last three decades. We were able to address this question because of the dedicated fieldwork of hundreds of citizen-scientist participants in the BFL project like you, who have returned detailed data on thousands of study sites across the continent and, in particular, the East.

We bolstered some of these data with other citizen-scientist collected data on thrush abundance from the Breeding Bird Survey, as well as with data on soil properties collected by the Natural Resources Conservation Service, and with data on acid deposited in precipitation from the National Atmospheric Deposition Project. After controlling for a number of such influences on Wood Thrush distribution, we were able to show that these thrushes were less likely to attempt to breed at sites that received highly acidic rain. We documented this finding in a paper in the prestigious Proceedings of the National Academy of Sciences that also suggested further study of this problem was needed. The reasoning was simple: while our paper pointed out a pattern of decreased probability of breeding with increasing acid deposition, the physical and biological processes that lead to this pattern remained unclear.

So, BFL scientists began fieldwork in 2002 at forty sites across New York state with two goals in mind. The first was to help increase our understanding of the role that acid rain, soil pools of calcium, and calcium-rich prey species might be having in the decline of the Wood Thrush. (Calcium-rich prey may be very important to breeding thrushes because females experience a tremendous demand for calcium when laying a clutch of eggs and many prey species, such as insects, contain little calcium.) The second goal was to develop and test a protocol that could be used by BFL participants to help us understand the mechanisms behind the effects of acid rain-the processes that lead to the pattern-across a wide geographic range. What we found was strong links between the number of calcium-rich prey such as snails, slugs, millipedes, and sow bugs and several soil properties such as its pH (acidity) or calcium content. The other result from our work is this simple protocol, which we think will result in data that will give us a much greater understanding of how acid rain effects birds in North America, information that may be crucial for future conservation efforts.