Recent analyses indicate that hoary bats (Lasiurus cinereus) may be at risk of significant population decline due to fatalities from collisions with wind turbines (Friedenberg & Frick 2021; Rodhouse 2015). However, uncertainty around hoary bat population estimates and wind energy buildout scenarios complicates the development of adaptive management targets. Here, we offer a method for calculating a fatality threshold based on the best available science. This scalable approach uses a nationwide annual fatality target and current wind energy buildout to allocate hoary bat fatalities across wind energy facilities based on their size, producing a per-megawatt fatality rate that might maintain a stable hoary bat population. We relied upon the expert-derived population size estimates and growth rates reported in Friedenberg and Frick (2021), estimated in the absence of mortality related to wind turbines. Finally, we calculated the percent reduction in fatalities needed to meet this threshold at two facilities beginning to implement adaptive management in the Altamont Pass Wind Resource Area. As wind energy scales up in California and elsewhere, continued research and creative solutions will be needed to effectively mitigate the potential adverse impacts of wind turbines on bat populations.

Katrina Smith is a Senior Environmental Scientist with California Department of Fish and Wildlife. She writes status reviews for terrestrial wildlife species petitioned for listing under the California Endangered Species Act. She also leverages her expertise in bat biology to assist CDFW with other needs relevant to at-risk species and serves as co-chair of the California Bat Working Group. She holds a M.S. in Natural Resources: Wildlife from Humboldt State University and a B.S. in Ecology and Environmental Biology from University of Wisconsin-Eau Claire.