Thousands of protected bald and golden eagles in America are expected to be killed by wind farms, after the companies were given a green light to operate high-speed turbines for up to 30 years.
Under the new rule by the Obama administration, wind companies and other power providers will not face a penalty if they kill or injure up to 4200 bald eagles, nearly four times the current limit.
Deaths of the more rare golden eagles would be allowed without penalty so long as companies minimise losses by taking steps such as retrofitting power poles to reduce the risk of electrocution.
The new rule, finalised on Wednesday, will conserve eagles while also spurring development of a pollution-free energy source intended to ease global warming, Fish and Wildlife Service Director Dan Ashe said.
"No animal says America like the bald eagle," Ashe said in a statement, calling recovery of the bald eagle "one of our greatest national conservation achievements."
Ashe said the Fish and Wildlife Service is trying to balance energy development with eagle conservation.
Wind power has increased significantly since Obama took office, and wind turbines as tall as 30-story buildings are rising across the country.
The wind towers have spinning rotors as wide as a passenger jet's wingspan, and blades reach speeds of up to 170 mph (273.5 kmp) at the tips, creating tornado-like vortexes.
The surge in wind power has generally been well-received in the environmental community, but bird deaths - and eagle deaths in particular - have been a source of contention.
The new rule is set to take effect in mid-January, days before Obama leaves office and while President-elect Donald Trump could change the rule or scrap it, the process would likely takes months or years.