Post-construction monitoring across North America consistently finds Lasiurus cinereus as the most frequently recovered carcass at wind energy facilities, alongside eastern red and silver-haired bats. All three are solitary, migratory, tree-roosting species; cave-hibernating bats are recovered far less often.
Collision alone does not explain the pattern. Thermal and near-infrared video shows bats approaching and circling monopoles and slowed rotors, with behaviour consistent with investigating a tall structure as a potential roost or a landmark. Deaths cluster in late summer and autumn, during migration and mating, and on low-wind nights. Some deaths result from barotrauma near the blade tips rather than direct impact.
The mitigation that works is unglamorous. Raising the cut-in speed, so that turbines do not spin during the low-wind conditions when bats are active, reduces fatalities substantially at modest energy cost. What is not resolved is the size of the continental hoary bat population, which makes it hard to say what proportion of the species is affected.