Abstract
Projected global growth in wind energy development has the potential to negatively affect wildlife populations, and yet the indirect effects of wind turbines on wildlife (e.g., displacement from otherwise suitable habitat) remain largely understudied, compared with investigations of direct effects (e.g., collision mortality). Thus, over a 3-yr period (2009–2011), we used 2 alternative survey methods to study displacement in breeding grassland songbirds at an operational wind facility in the southern Great Plains, USA. Using a line transect method in 2009 and 2010, we estimated the densities of Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows(Ammodramus savannarum) within 500 m of wind turbines. Dickcissel density was positively related to vegetation structure and was highest 301–400 m from wind turbines in both years; however, this relationship was confounded by fence lines bisecting transects within this single distance bin. By contrast, we found no such relationships in Eastern Meadowlarks or Grasshopper Sparrows. Using a plot-based method in 2011, we estimated Dickcissel and Grasshopper Sparrow densities within 750 m of wind turbines. Again, we found a strong positive relationship between Dickcissel density and vegetation structure. With the change in survey method, however, the confounding effect of fence lines was removed and the relationship between distance to turbine and Dickcissel density disappeared. Variation in Grasshopper Sparrow density in 2011 was not explained by any variable we measured. In summary, we found no evidence of displacement within 500–750 m of wind turbines in the 3 most abundant breeding grassland songbirds at our site. We caution that it may be difficult to isolate the effect of distance to turbine from other factors that covary with distance (e.g., presence of fence lines) when using a line transect method to study displacement at operational wind facilities.