Bats require an atypical approach when being studied to predict the impacts of a new wind farm. The right equipment includes ultrasonic microphones to record the animals' echolocation.
So you're surveying birds, turtles or flowers in an area proposed for new wind turbines. Pack the standard equipment: binoculars, hiking boots and notebooks. Find a good spot. Start counting.
But bats, given their nocturnal activities, require a different approach. Your eyes can't track movements of winged creatures against a dark sky, and even listening intently won't pick up the high-pitched clicks and other sounds that bats emit in their sonar search for food and other targets.
Look closely at the data, however, and you'll find everything you need — quietly, safely and unobtrusively.
"We use ultrasonic microphones to record their echolocation," says Jeff Miller, a wildlife biologist at Burns & McDonnell, who employs arrays of SM-2 Bat Detectors to collect sounds to create spectrograms for analysis. "I can look at a spectrogram and tell what a bat is doing — whether it's passing through, foraging or successful in capturing prey — or even what species it is. It's a noninvasive way to sample bats and bat activity."
The sounds helped Burns & McDonnell forward environmental reports to EDF Renewable Energy (EDF RE), a company looking to add up to 62 wind turbines in an area spanning 22,400 acres in Pipestone and Murray counties in southwestern Minnesota.
EDF RE told state regulators that such reports would help the company "design the turbine layout, access roads, substation, interconnection facilities and laydown areas to minimize the impact on birds, bats and wildlife habitat."
Miller's focus: the potential presence of the Northern long-eared myotis bat, a species designated for "special concern" by the state of Minnesota.
For six months Miller recorded from 30 minutes before sunset to 30 minutes after sunrise, capturing vocalizations, clicks and other high-pitched bat sounds. Microphones near ground level worked with others perched 145 feet above, the level typical for rotor sweeps of commercial wind turbines.
Of the 4,917 bat passes recorded at three monitoring locations, 26 were attributed to myotis bats — but likely not the Northern long-eared variety. The study, Miller told EDF RE, shows that the site possesses a low risk for harboring bats of particular concern.
"We're helping EDF RE minimize any impacts to any sensitive species in the area," he says. "This allows them to make a sound choice on how to use the area for harnessing wind."