Acid Rain and Wood Thrush Populations
Recent research by scientists from the Cornell Laboratory of Ornithology provides stronger evidence that acid rain contributes to declining Wood Thrush populations.
Understanding the Risk to Neotropical Migrant Bird Species of Multiple Human-Caused Stressors: Elucidating Processes Behind the Patterns builds on elements of their previous research by considering habitat fragmentation as an additional human causal factor influencing Wood Thrush populations.The Wood Thrush is a Neotropical migrant common to the Eastern United States. Forests along the Appalachian Mountain chain from New England to Georgia are a preferred habitat. Past research on Wood Thrush population declines have focused primarily on single issue causes, with habitat fragmentation and acid rain receiving a good deal of attention.
The logic of the relationship between habitat fragmentation on bird populations is relatively straight forward. Whenever there is a loss of forested areas due to road building or other development projects, forest birds such as the Wood Thrush lose potential breeding grounds and population decline follows.
Acid rain is the general term given to the wet and dry deposition of acidic materials, such as nitrogen oxides (NOx) and sulfur dioxide (SO2), emitted into the air by the burning of fossil fuels such as coal and gas. When the acidic materials fall to the ground, they alter soil pH, increasing its acidity. Research on Wood Thrush population starts with the hypothesis that changes in soil composition brought about by acid rain alters insect populations. Breeding Wood Thrush, dependent on a diet of calcium rich insects to produce healthy eggs, are hypothesized as the secondary victims in this ecological chain of events.
One problem with the single cause studies is their lack of ability to differentiate between the relative strength of the factors under consideration. For example, it is possible that the results from previous research examining the relationship between acid rain and Wood Thrush populations were influenced by habitat fragmentation factors not accounted for in the research methodology.
The Cornell researchers took this issue into account for their study. Their methodology consisted of choosing four different locations in New York state that shared many similar habitat characteristics. By doing so, they could use habitat as a natural control variable to highlight the effect of acid rain as a factor in Wood Thrush populations. First and foremost, all four areas were large tracks of forest areas with a wide variety of soil types.
Under this controlled environment, the researchers still found a significant relationship between soil pH level, the presence of calcium rich insects, and breeding Wood Thrush populations. They suggest that their methodology serves as a useful starting point for conducting a series of similar research projects across a broader geographical area.
© 2007 Patricia A. Michaels