Spatial Pattern of Summer Bat Mortality from Collisions with Wind Turbines in Mixed-grass Prairie

Abstract

Spatial analysis that aims to identify site-specific hotspots of collision mortality from birds or bats striking wind turbines can potentially lead to mitigating measures that reduce mortality rates. During May–Jul. 2004 and 2005, we studied bird and bat mortality from collisions with wind turbines at a 102 megawatt, 68-turbine wind farm in the southern Great Plains, Oklahoma, USA. Standardized searches around turbine bases yielded 122 total carcasses of which 92 (75%) were found within 20 m of the turbine bases. We identified 111 carcasses of seven species of bats and 11 carcasses of 6 species of birds. Brazilian free-tailed bats (Tadarida brasiliensis) comprised 85% of bat carcasses collected. We corrected turbine collision estimates using searcher efficiency trials and a range of removal (i.e., “scavenging”) rates reported in the literature. Estimated bat turbine collisions ranged from 1.19–1.71 fatalities/turbine (1.03–1.37/megawatt). These data provide some of the first evidence for a steady rate of collision mortality of Brazilian free-tailed bats at a North American wind farm, most likely due to the site's proximity (∼15 km) to a maternity colony. Spatial analyses indicated no consistent pattern in mortality estimates relative to ground cover or topographic position; but collision mortality was higher at several individual turbines, all of which were located near the heads of eroded ravines.