Do black turbine blades really spare birds? It's complicated

Norwegian research that found painting wind turbine blades black lowered bird fatalities by a whopping 72% has sparked enormous U.S. interest, but experts say replicating the study could take a long time in North America, where wind power is booming.

Turbines' impact on birds is a bruise on wind energy's reputation, sparking warnings that the sector's growth threatens a wide range of avian species. 

The wind industry has spent millions of dollars on efforts to reduce threats to birds — from speakers that emit noises meant to deter an approaching bird to paying biologists to keep watch for eagles.

But the Norwegian Institute for Nature Research study pointed to a potential low-cost solution: Painting one of a turbine's three turbine blades black dramatically lowered bird mortality. The study's August publication in Ecology and Evolution generated headlines around the world (Greenwire, Aug. 25).

That sounds great, experts say, but it's just one study.

"It's a single data point and small single data point," said Stu Webster, senior manager of technology innovation and research at the American Wind Wildlife Institute (AWWI). "The primary caveat from the authors is that it needs to be replicated in order to strengthen it."

On its face, the study's premise is simple.

Rotating turbines create a blurring effect that may trick birds into believing there are no obstacles moving across their path. But painting one blade black seemed to lessen that blur.

The Norway study was inspired by laboratory research from a University of Maryland psychology professor, William Hodos, a leader in bird-vision research. His 2003 report, supported by the National Renewable Energy Laboratory, showed painting a single turbine blade black was the most "encouraging" of a variety of paint patterns at reducing "motion smear" for the American kestrel, a small bird of prey.

Norwegian researchers broadened the Maryland kestrel study by removing it from the lab. But they kept its scope limited, treating just four turbines at the 68-turbine Smøla wind farm on Norway's eastern coast.

The turbine farm was Europe's largest when it was commissioned and provided several years (2006-2016) mortality data before and after the blades were painted in 2013.

Trained dogs, passersby and wind technicians kept a tally of post-painting mortality. There was an average of 71.9% reduction in yearly fatalities from blade collisions at the painted turbines and a 50% reduction in collisions with those turbine towers, researchers said.

"From a design standpoint, it was really rigorous," said John Lloyd, AWWI's associate director of research. "It's a really good start. What comes next is the question of, to what extent can we generalize these results with other species?"

Does geography matter?

The U.S. wind industry provided just over 7% of the nation's power last year, but it is rapidly expanding. In 2000, the U.S. had just 2.53 gigawatts of installed wind capacity, according to the Department of Energy, but that tally could rise to 404.25 GW by 2050.

The industry, however, has a bird problem. It is estimated to kill between 140,000 and 500,000 birds a year, according to the Fish and Wildlife Service. And bird advocates say the tally may be higher. 

But if you search the ground at a single turbine, you might find one dead bird in a year, said Taber Allison, director of research at AWWI.

That doesn't mean there aren't more, Allison said. For a variety of reasons, the carcasses aren't always seen. Predators eat or move them, carcasses decay and get hidden by dust, birds fall outside the search areas. And then there's simple human error.

The Norway study's limited sample size of dead birds per turbine poses a big problem for generalizing findings. And it's one of several problems.

Among others cited by researches: Does geography matter? Topography? How much solar heat does a black blade absorb, and what impact does that have on the specifications for these machines?

And there's a regulatory hurdle. The Federal Aviation Administration requires turbines to be painted white or light gray for best visibility. The agency would have to waive that regulation for a study and consider much broader adjustments if the Norway findings were ever found to be effective enough to be deployed at scale.

An FAA spokeswoman said the agency had not yet received requests for a replication of this study but noted there is a process for potential regulatory exemptions.

Despite industry and scientific interest in the Norway study, Allison said, repeating it may require jumping many hurdles and take several years.

Eagle deaths at Altamont Pass

Industry has looked at painted blades before, and results weren't good. "The trials didn't yield promising results," Allison said. "Interest petered out and turned elsewhere."

Michael Speerschneider, senior director of permitting policy and environmental affairs at the American Wind Energy Association, said the perception of turbines as bird killers stemmed from some early research at the Altamont Pass wind farm east of San Francisco.

The study examined several wind farms, totaling more than 6,000 turbines of 1980s vintage that were smaller than their modern counterparts and placed much closer together.

The National Audubon Society estimates as many as 110 golden eagle deaths a year at the site, among thousands of annual bird deaths.

"[Altamont] has driven some of the [negative] perception," Speerschneider said. "But that was really one area. There were [other wind farms] even in California that didn't have that kind of result."

Speerschneider noted that Altamont Pass represented a lesson learned for the wind sector and precedes promulgation of Obama-era guidelines from FWS that are widely used today. But the public excitement surrounding the Norway research may salt oil industry wounds.

Less culpable for bird mortality than power lines and all-glass buildings, wind kills fewer birds than other energy industries, like the oil patch, which takes up to 1 million birds every year in its open-air wastewater ponds, according to the top end of FWS estimates.

"The perception is — and maybe that's why there's interest in [the study] — that wind energy has large impacts on birds, and this could solve that," Speerschneider said.

But the underlying premise of a big problem isn't accurate, he said, noting that an expanded version of the Norway experiment would be necessary for industry to be sure it was effective.

'Not a panacea for bird deaths'

But Shawn Smallwood, a California ornithologist and expert in bird mortality from energy infrastructure, echoed the call for more study.

"I respect the authors of the paper, having interacted with them on wind and wildlife for a decade," the ornithologist said in an email. "Regardless, I have reservations about the paper's conclusions."

Smallwood, who was party to the early research at Altamont Pass, noted that Hodos' research was specific to the "special visual acuity of raptors for detecting motion at far distances."

"The effect shouldn't apply to other birds, many of which collide with turbines at night when the black blade is irrelevant," he said.

The Norway study also pooled the dead bird species into one category in order to have a reasonable sample size for turbine collisions, which makes it impossible to read the effect on any single bird species, he noted. Smallwood also critiqued some design elements of the Norway study that could have affected findings, such as the lack of carcass detection trials.

Other bird researchers and observers had their own concerns about the study's findings.

"Even if the painting works eventually, its overall effect on most species is unknown at this time," the Black Swamp Bird Observatory of Oak Harbor, Ohio, wrote in a statement after the study's publication. "Perhaps these are reasons why the work done in 2003 has languished for almost 20 years and still has not come to practical fruition. So, painting the blades is certainly not a panacea for bird deaths at turbines."

Roel May, one of the Norwegian study's authors, acknowledged the limitations of the research.

"At Smøla, we dealt mostly with day-active bird species, with a main focus on the white-tailed eagle. What we do not yet know is to which extent the measure could help reduce collision fatalities of nocturnal migration, for instance," he said. "We do not know how efficient it will be at other sites with different topography and habitat, and different bird species assemblages."

Roel said he wasn't party to any follow-up studies but had communicated with researchers in several countries interested in replication, from Portugal to the Netherlands.

In the U.S., scientists say they aren't deterred by the narrow scope of the Norwegian research. If anything, the remaining questions and challenges are accelerating attention, several scientists said. "That's the thing about this paper; it's reignited that interest," AWWI's Allison said, echoing others in the wind and wildlife field. "It calls for replication, and I think it's worth replicating."