Secretary of the Interior Ryan Zinke claimed Tuesday that wind farms kill up to 750,000 birds a year.

Verdict: Unsubstantiated

Although estimates vary widely, the figure cited by Zinke is certainly plausible. Bird deaths due to wind turbines pale in comparison to deaths by other man-made structures like glass buildings and communication towers.

Fact Check:

The number of wind farms operating in the U.S. has increased drastically in the last two decades. Today, over 52,000 wind turbines supply about 6 percent of the country’s energy needs and have enough capacity to power 25 million homes.

A consequence of that development is an increase in what researchers have called “avian mortality.”

The average wind turbine stands 280 feet tall with blade tips spinning somewhere between 138 mph and 182 mph under normal conditions. Despite efforts to reduce the risk of injury and death, birds are inevitably killed mid-flight.

Fossil fuel advocates will often point to these collisions to argue that renewable energy also comes at an environmental cost. “We probably chop us as many as 750,000 birds a year with wind, and the carbon footprint on wind is significant,” Zinke said at an energy conference in Houston.

That’s a pretty striking statistic – but are the number of deaths really that high?

It turns out the answer isn’t all that clear cut. “Estimates of bird/turbine collision range widely and all of the studies attempting to quantify this contain some level of bias and uncertainty,” reads the Fish and Wildlife Service (FWS) website.

Although bird fatalities have been studied at some wind facilities, there are relatively few data points, and researchers lack studies for major parts of the country. By one estimate, 86 percent of wind farms (by capacity) had not been investigated as of 2014.

“A statistician would approach such a sample either with considerable caution and a host of caveats, or with a blindfold of optimism,” reads a paper on bird fatalities co-authored by three leading researchers.

Nonetheless, these researchers have each published studies that are generally regarded as the most comprehensive and statistically sound estimates available today.

Two of the studies arrived at somewhat similar conclusions – one paper estimated 140,000 to 328,000 bird fatalities in the U.S. per year, while another calculated somewhere between 214,000 and 368,000 fatalities annually (including Canada). The third study estimated a much higher range of 467,000 to 679,000 bird fatalities a year.

The variation depends on several factors including modeling techniques, the design of the turbines assumed and which studies the authors chose for inclusion in their models. The third estimate is higher, in part, because it included lattice-style turbines that birds can perch on, while the other two studies excluded them, arguing that these turbines were being phased out.

It’s possible the underlying data may underestimate bird fatalities because most data points come from the wind industry itself.

“Because fatality studies generally are conducted by or financially supported by the wind industry, a skeptic might question if results of studies demonstrating high rates of fatalities are made as easily available as results from innocuous wind farms,” reads the review paper.

When asked how Zinke came up with a figure as high as 750,000, the FWS acknowledged that there are no peer-reviewed estimates quite that high, but pointed out that the studies in question were published years ago and rely on data from 2012. “The most recent paper we have isn’t that recent,” Gavin Shire, chief of public affairs for the FWS, told The Daily Caller News Foundation.

Wind energy capacity has increased substantially since 2012, rising from 60,000 megawatts (MW) to 89,000 MW today – a 48 percent change. “The 750,000 number is an effort on our part to try to bring those numbers up to date,” Shire said.

TheDCNF got in contact with the authors of two out of the three studies to determine whether the internal estimate by the FWS was reasonable.

The researcher with the highest estimate, Shawn Smallwood, agreed that his figures were outdated and now believes that fatalities are actually higher than the FWS estimate. “I would put the current wind energy impact on birds at about one million fatalities per year,” he said in an email.

Scott Loss, the researcher who calculated the lowest estimate, believes the number of fatalities has certainly grown in the last five years, although to what extent is obviously up for debate.

He emphasized to TheDCNF that whatever the number may be, wind turbine fatalities are small relative to other sources of bird collisions. Birds are killed far more often by other man-made structures like communication towers, electrical lines and building glass, according to the FWS website.

And environmentalists are quick to point out that it’s not just renewable energy sources that cause bird fatalities: oil fields kill up to 1 million birds a year.

In a bid for American “energy dominance,” the Trump administration has pushed to increase natural gas exports and moved in January to open more coastal waters to offshore drilling.

“All energy has its consequences,” Zinke said at the conference. “My job is to make sure all of the above – we balance it – and make sure that innovation, best science, best practices are incorporated into our energy portfolio.”

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