Predictors of Bat Mortality Rates at North American Wind Facilities and an Evaluation of Biases Influencing Mortality Estimates

Abstract

Wind energy helps close the gap between energy production and energy consumption; however, it is not entirely environmentally neutral as there are several indirect and direct impacts to birds and bats. The primary direct impact for bats is mortality by collisions with wind turbines. Several cross-site syntheses of bat collision data have resulted in national fatality estimates that vary by more than an order of magnitude (33,000 to 888,000 bats per year). However, no research has taken a national-scale approach to assess spatial, seasonal, and taxonomic variation in bat mortality and to evaluate the methodological factors that influence mortality estimation. I completed an exhaustive review of the published and unpublished literature on bat collisions with wind turbines and extracted data from 218 post-construction mortality reports representing 100 U.S. facilities and 12,000 bat fatality records. This database was used to conduct a national-scale meta-analysis to (1) Identify wind facility-scale correlates of bat collision mortality rates, (2) Assess how differences among studies in study design, data collection, and statistical analysis contribute variation to wind facility-scale estimates of mortality, and (3) Based on those analyses, identify specific study design, data collection, and analysis steps that should lead to relatively unbiased estimates of bat fatality rates. Information from these systematic data-driven analyses � the first of their kind to be based on a national data set of this size � will be useful in considering locations of future wind farms, designing mortality monitoring protocols, and ultimately, improving our understanding of impacts of wind facilities to bat populations.