At most wind farms, the turbines remain still until the wind reaches a speed of about 8 to 9 miles per hour, called the cut-in speed. Arnett and his colleagues found that increasing that speed to roughly 11 mph reduced bat deaths by at least 44 percent, and by as much as 93 percent if the cut-in speed was set at 14.5 mph.
The study was done during the migratory period, when winds are typically lower, and thus the turbines are producing less energy, so the loss of production was estimated at only around 1 percent annually.
The researchers monitored sites across the Appalachian Mountain region and found that the bat-kill rate was up to 5.4 times lower at sites where the turbines were operating at the higher cut-in rate.
Most of the bats killed by turbines are migratory tree bats, including hoary and silver-haired bats. Each fall they migrate from Canada and the northern U.S. to the southern U.S. or Mexico.
Granted, they aren't as pretty as birds. But they are important, and they need help.