Bird and bat responses to wind energy development in Iowa
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Most previous studies of wind energy's impacts on wildlife in the United States have measured direct mortality. Yet it is known that wind energy can also indirectly impact birds and bats by altering habitat use around the turbines. The overall goal of this study was to investigate the indirect impacts of wind turbines on birds and bats in primarily agricultural portions of Iowa.This was accomplished by 1) documenting bird use at wind farm sites in Iowa by estimating the density of breeding birds in relation to proximity to turbines, 2) assessing the relationships between the nest survival of Red-winged Blackbirds (Agelaius phoeniceus) and proximity to turbine, and 3) monitor bat activity patterns bear wind turbines to determine if proximity to turbine affects activity of bats. We conducted 1,880 point counts to monitor bird use at varying distances to turbines and at paired control sites. We documented avoidance behavior (particularly with grassland and generalist species, including Dickcissel, Common Yellowthroat, Red-winged Blackbird, and American Robin), attraction behavior (mostly in agricultural species, and especially in Killdeer) and multiple examples of species unaffected by turbine proximity (including Song Sparrow and Common Grackle). We monitored 538 Red-winged Blackbird nests during 2011 and 2012. Wind turbine proximity had negligible effects on a generalist species in Iowa, with a non-significant effect of turbine proximity for the nestling stage, with slightly higher survival closer to turbines. Bat activity was monitored at 71 points in Story County, Iowa during 2011 and 2012. Activity was more likely on nights with lower wind speeds, higher temperatures, and a full moon, and at points further from turbines and closer to woodlots. The amount of activity depended on the day, with activity peaking mid-July, and was greatest on nights with lower wind speeds, higher temperatures, less precipitation, and lower barometric pressures, and at points closer to woodlots and rivers. By broadening our understanding of the indirect effects of wind turbines to include behavioral responses, avian nest survival, and bat activity we can refine siting guidelines that will limit the effects of wind farms on the surrounding habitat while still offering the benefits of "green" energy.