Spatiotemporal patterns in sex ratios of bat fatalities at wind energy facilities in the United States

Abstract

A challenge facing bat conservation and wind energy development is how to maximize renewable energy production while minimizing impacts to bat populations. Reproductive-aged females are particularly important to dynamics and stability of bat populations due to their life history characteristics, but morphological sex identification methods have resulted in inaccurate reporting of sex ratios of fatalities at wind energy facilities. Our goal was to assess overall species-specific sex ratios of fatalities, and how those ratios varied by time and location. We used molecular techniques to determine the sex of 4445 carcasses of Brazilian free-tailed (Tadarida brasiliensis), evening (Nycticeius humeralis), hoary (Lasiurus cinereus), eastern red (Lasiurus borealis), northern yellow (Lasiurus intermedius), silver-haired (Lasionycteris noctivagans), and southern yellow (Lasiurus ega) bats found during turbine searches at 20 wind energy facilities in ten states in the United States between 2009 and 2022. Species composition and number of years of data varied by site. Overall, there were more fatalities of females than males for silver-haired and southern yellow bats, but not the other species. Brazilian free-tailed bat sex ratios were female skewed in late summer, whereas female skew occurred during portions of spring and summer/fall for eastern red bats, hoary, and silver-haired bats, and in spring and late fall for evening bats. In addition, spatial patterns in sex ratios existed for eastern red and hoary bats. The observed spatial and temporal patterns of fatalities can help target fatality reductions strategies to locations and times of year that maximize the conservation benefit of those actions.