Getty Images

Interior Secretary Ryan Zinke told the CERAWeek energy conference in Houston on Tuesday that "there's no such thing as free energy," which is undeniably true. But in arguing that the costs were roughly equal for various forms of energy production, he marshaled some alternative facts.

"Certainly oil and gas and coal have a consequence on carbon," Zinke told the oil and gas executives and others at the conference. But solar energy takes land out of use for recreation and hunting, he said, and "we probably chop us as many as 750,000 birds a year with wind, and the carbon footprint on wind is significant."

President Trump has attacked wind farms, claiming in 2016 that "more than 1 million birds a year" die with wind energy. But like Trump, "Zinke is exaggerating the figure beyond virtually all published estimates," says Amy Harder at Axios, and "turbines are a drop in the bucket when it comes to the human-related causes of bird deaths." Also, over their life cycles, wind turbines generate up to 3 percent of the greenhouse gas emissions that coal does and 7 percent of the emissions from gas-fired electricity.

According to the U.S. Fish & Wildlife Service, a part of the Interior Department, the "most comprehensive and statistically sound estimates" put the number of birds killed in wind turbines at 134,000 to 437,000 a year. That number will grow as wind generation expands, but for context, a 2012 Bureau of Land Management memo estimates that 500,000 to 1 million birds die each year in oilfields. "Regardless of the estimate, wind turbines rank much lower than many other human-caused threats in terms of total birds killed," says University of Oklahoma professor Scott Loss.