Wind turbines killed at least 600,000 -- and possibly as many as 900,000 -- bats in the United States in 2012, researchers say.

Writing in the journal BioScience, the researchers said they used sophisticated statistical techniques to infer the probable number of bat deaths at wind energy facilities from the number of dead bats found at 21 locations.

Bats, which play an important role in the ecosystem as insect-eaters, are killed at wind turbines not only by collisions with moving turbine blades but also by the trauma resulting from sudden changes in air pressure that occur near a fast-moving blade, the study said.

Study author Mark Hayes of the University of Colorado notes that 600,000 is a conservative estimate -- the true number could be 50 percent higher than that -- and some areas of the country might experience much higher bat fatality rates at wind energy facilities than others.

Hayes said the Appalachian Mountains have the highest estimated fatality rates in his analysis.

With bats already under stress because of climate change and disease, in particular white-nose syndrome, the estimate of wind turbine deaths is worrisome, he said -- especially as bat populations grow only very slowly, with most species producing only one young per year.