Montana Fish, Wildlife and Parks is leading a study of how a NorthWestern Energy-owned wind farm called Spion Kop is affecting bats and birds east of Great Falls.
One of the initial findings is that the project has been harder on bats than a pre-construction study predicted, with bats possibly mistaking the turbines for trees.
But no raptor carcasses have been discovered, with NorthWestern crediting upfront investigation into the location of raptor nests prior to the siting of giant turbines with blades that can spin up to 190 miles per hour.
It’s the first time a state agency, as opposed to a private developer, has conducted a so-called post-construction study, and the data on the number of birds and bats killed, usually closely guarded, will be made public when it’s completed.
NorthWestern, the state’s largest public utility, hired FWP to do the two-year study, which Sam Milodragovich, a NorthWestern Energy biologist known as the “birdman," says is "the right thing to do."
"If we build something we want to build it right," Milodragovich said. "We want to know what the risks are and how we can minimize the impacts."
Utility and FWP officials say the study will lead to better understanding of how wind farms affect wildlife that could lead to improve siting and layout of future wind projects.
Spion Kop is seven miles northeast of Raynseford and 35 miles east of Great Falls.
The 40-megawatt wind farm with 25 General Electric turbines became operational in 2012. Developer Compass Wind sold the project to NorthWestern upon its completion. GE now operates it for NorthWestern.
Compass Wind committed to siting turbines a quarter mile away from raptor nests, and moved two turbine locations based on that guideline, Milodragovich said. And NorthWestern encouraged additional agency consultation and studies after buying the Spion Kop project.
“If you don’t do that upfront work, you can’t make these decisions,” said Milodragovich, adding NorthWestern is proud of the wind farm.
NorthWestern must purchase renewable energy projects including wind farms to meet state-mandated green-energy requirements.
Preconstruction work for many wind farm proposals he’s reviewed hasn’t impressed Milodragovich.
That dissatisfaction is one reason NorthWestern hired FWP to lead the study at Spion Kop, he said.
“Generally, we don’t see very many thorough pre-construction investigations,” Milodragovich said.
The utility hopes that the post-construction study at Spion Kop will give FWP hands-on experience at wind farms so it and other agencies can speak with authority when developers seek input prior to the development of future projects.
“The other piece is we have to protect our ratepayers,” Milodragovich said.
In 2014, PacifiCorp Energy paid a $2.5 million fine, and Duke Energy, $1 million, after wind farms in Wyoming killed migrating raptors.
In February 2015, NorthWestern contacted FWP to conduct the post-construction monitoring.
FWP hired Kim Linnell, a conservation technician, in May 2015 to lead the project. Two years of post-construction monitoring began in 2016, with the search season May through October.
“We definitely want wind to proceed and succeed, but with as minimal impact as possible,” Linnell said.
Recommendations in the U.S. Fish and Wildlife Service’s Wind Energy Guidelines are being followed in the post-construction study. It involves systematically searching the ground around 10 of the 25 turbines for carcasses of bids and bats that have fallen after striking turbine blades, Linnell said.
The wildlife survey conducted prior to the construction of the wind farm was an attempt to predict what the impacts could be.
“Now we’re trying to see if these predicted impacts are correct,” Linnell said.
Hoary and silver-haired bats are the two primary bat species that migrate through the the Spion Kop area.
A preconstruction acoustic survey for bats predicted that the wind farm’s impact would be low, but the preliminary results of the study show it’s been higher than anticipated.
Over the first six months of the post-construction study, FWP is estimating with 95 percent confidence that the turbines killed between 120 to 397 bats with the figure likely 221 or about nine bats per turbine.
Those results prompted a second year of monitoring.
“So knowing reproductive biology, we do believe it’s something to be concerned about,” Linnell said.
Bats are long-lived and produce one to two pups a year, and are not rodents, she said.
Cumulative impacts on bats from multiple wind farms over a wider area is a concern, she added. And bats don’t have the same protections as birds from federal laws such as the Migratory Bird Treaty Act, she noted.
“Research is showing bats are attracted to them,” Linnell said of the wind turbines.
The large blades may not appear to be spinning that fast, but the maximum tip speed is 197 mph.
Bats are naturally curious, Linnell said.
And they will swarm in trees during migratory season.
Both may be factors in why bats are attracted to the turbines, Linnell said.
It’s not clear if the bats perceive the turbines as trees and a potential food source, Linnell said.
Migration begins in July and extends into September.
“And the activity really peaks at that time, and that also correlates with when we find bat mortality,” Linnell said.
Last year, the searchers didn’t find the first bat fatality until July.
At the wind farm, two acoustic bat detectors monitor bat activity.
FWP has found that the bats are most active during nights when it’s less windy and warm.
That is important information because it could lead steps to limit the impacts, Linnell said.
One possibility to reduce bat deaths is implementing an "operational curtailment" at the wind farm during bat migration. The wind turbines usually power on and begin turning at a certain wind speed. That starting wind speed could be increased during bat migration, which would mean that the turbines would not begin spinning until it becomes windier. As a result, the turbines wouldn't be turning on less windy nights when the bats are most active.
Over the first six months of searching, 27 bat carcasses and one live bat were found.
But two factors bias raw counts of birds and bats, Linnell said.
One is that not all of the carcasses, which are small and difficult to spot in tall grasses, are found.
The second bias that needs to be accounted for is “carcass persistence.” In other words, scavengers such as birds or coyotes could carry off some of the carcasses.
“So we have to account for both of these biases,” Linnell said.
Adjusted for those biases, FWP is estimating 221 bats were killed over the six-month period.
The 40-megawatt Spion Kop wind farm has 25 turbines.
The 40-megawatt Spion Kop wind farm has 25 turbines. It is located seven miles northeast of Raynesford. (Photo: Karl Puckett)
“We honestly don’t know what the potential impacts are,” Linnell said.
Based on pre-construction surveys at Spion Kop, it was predicted that mortality for raptors would be modest but no raptor carcasses have been discovered.
Red-tailed, ferruginous and Swainson’s hawks and golden eagles nest within 10 miles of the wind farm.
Two western meadowlarks were found over six months. Accounting for bias, that’s 14 small birds over six months.
Post-construction monitoring at Spion Kop is overseen by a technical advisory committee consisting of the U.S Fish and Wildlife Service, FWP, and Montana State University professor, a bat researcher and NorthWestern.
FWP will give recommendations to NorthWestern at the conclusion of the project.
Working closely with state and federal agencies gives NorthWestern credibility it might not otherwise have, Milodragovich said.
“When I go talk to the agency, they believe what I tell them,” he said.
FWP often has to communicate with wind farm builders so it’s a good idea for the agency to get on-the-ground experience on the impacts of wind farms, Linnell said.
The study also will assist the agency in collecting and interpreting data and providing feedback to developers as more wind projects are proposed, Linnell said.
“We’ve never been actually on the ground,” she said.
The post-construction study is the first in Montana by a public state agency as opposed to the developer, Milodragovich said.
And because a state agency is conducting the study, the wildlife information will be public, which Milodragovich considers one of the best aspects of the work. Publicly available information about the impacts of wind farms on birds and bats is “unheard of in the country,” Linnell added.
“It just made sense,” Milodragovich said.
One day in June, Linnell and Camille Waters and Chuck Taylor, FWP science technicians, traveled to the wind farm for the weekly search among the turbines for bird and bat carcasses.
They were joined Milodragovich.
Wind turbines are arranged in line that that ascends a ridge.
“Pretty good place to put a wind farm,” Milodragovich says.
May and June are the most difficult times to search for carcasses because dense vegetation makes them less visible. Most of the carcasses are intact when found.
“We even found a live bat last year on the ground,” Linnell said.
Square search plots are 160 meters-by-160 meters with turbines at the base. Research suggests most of the birds that strike turbine blades fall to the ground within 200 meters, and bats within 80 meters.
It takes an an hour to an hour-and-a-half to search each of the 160-by-160-meter plots.
On this day, they would be searching plots around three turbines, the equivalent of walking six miles.
“There’s stuff going on up here that hasn’t been done before,” Milodragovich says.
Taylor sticks an instrument into the air to check the temperature and wind speed, which is 13.8 mph. A “whooshing” sound can be heard from the twirling blades. The turbines are 397 feet tall from the ground to the highest tip of the blades.
They set off walking back and forth with hand-held GPS devices that tell them where to go. A great-horned owl is discovered in the grass.
But it’s a plant by Linnell.
Sometimes, Linnell places random carcasses on the landscape so searching efficiency can be accounted for in the calculations of the mortality estimates.
The information being gathered is "super useful," says Taylor, before he begins walking through the heavy grass, eyes trained on the ground.
“We still need to realize the effects of even a clean energy source,” Taylor says.