The goal of displacement research, such as studies conducted by WEST, Inc. and by the U.S. Geological Survey, Northern Prairie Wildlife Research Center (NPWRC), is to quantify the indirect impacts of wind projects on grassland-breeding songbirds over a rather large area. Ideally, data at multiple wind projects in grassland and shrub-steppe habitats should be collected in a standardized manner, with the overall objective of quantifying the level of displacement of breeding grassland and shrub-steppe songbird species. One hypothesis currently being tested with displacement research by WEST and NPWRC is that densities of grassland songbird species do not vary with distance from wind turbines. These researchers are also quantifying the extent of any displacement effects.
We advocate a focus on identifying possible reductions in densities of breeding songbirds, rather than on reproductive success, for three primary reasons. First, reproductive success tends to be highly variable spatially and temporally and is influenced by a variety of factors, which make it difficult to distinguish effects of individual factors such as proximity to wind turbines. Second, in most studies of reproductive success on study areas the size of wind farms, the sample sizes of nests are rarely sufficient to draw even tentative conclusions. And third, even if nesting is common, finding sufficient numbers of nests to assess reproductive success is challenging (Winter et al. 2003), requiring large investments in time and labor.