Apparently bats die at windmills. But the USGS scientists are on it.
"One research tool that is particularly well-suited to studying the origins of bats killed at wind turbines is stable isotope analysis. USGS scientists recently pioneered the application of stable hydrogen isotope analysis to the study of migration in terrestrial mammals and proved the efficacy of the technique for studying the continental movements of bats. Coincidentally, this groundbreaking research focused on the very same species of bat (the hoary bat, Lasiurus cinereus) that is killed most frequently at wind turbine sites across North America. Because of this, the USGS is in the unique position of having an existing framework of stable isotope data on which to build."
Coincidentally, later research revealed the hoary bats’ inability to detect windmills while stuffed with stable isotopes.