BUTTE, Mont. (AP) — At a former open pit copper mine filled with billions of gallons of toxic water, sirens and loud pops from propane cannons echo off the granite walls to scare away birds so they don’t land.

After several thousand migrating snow geese perished in the Berkeley Pit’s acidic, metal-laden waters in 2016, its owners deployed a sophisticated arsenal to frighten away flocks, including lasers, drones, fireworks and remote-controlled boats.

Montana Resources already had been hazing incoming birds with spotlights and rifle shots into the water — and a spokesman says those existing deterrents likely helped the company avoid a penalty or prosecution under the Migratory Bird Treaty Act.

But the Trump administration wants to end the 50-year practice of using the criminal penalties under the migratory bird law to pressure companies into taking measures like these to prevent unintentional bird deaths.

Critics — including top Interior Department officials from Republican and Democratic administrations — say the proposed change could devastate threatened and endangered species and accelerate a bird population decline across North America since the 1970s.

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Former U.S. Fish and Wildlife Service Director Dan Ashe told The Associated Press the law’s threat of prosecution served as “a brake on industry” that had saved probably billions of birds.

“Removing that obligation, if it stands, over the next several decades will result in billions of birds being casualties,” said Ashe, who served in the Obama administration. “It will be catastrophic.”

Industry sources kill an estimated 450 million to 1.1 billion birds annually, out of an overall 7.2 billion birds in North America, according to the U.S. Fish and Wildlife Service and recent studies.

The Trump administration dismissed Ashe’s dire prediction, contending companies will continue to avoid bird deaths voluntarily.

At the Berkeley Pit, Montana Resources plans to keep up efforts that drive away almost all birds, in part to avoid a repeat of the negative publicity and community backlash that followed the 2016 bird kill, according to Mark Thompson, the manager of environmental affairs.

“We as a company see it as an essential environmental protection,” Thompson said.

The 1918 migratory bird law came after many U.S. bird populations had been decimated by hunting and poaching, much of it for feathers for women’s hats. Over the past half-century, the law also was applied against companies that failed to prevent foreseeable bird deaths.

However, the Trump administration says deaths of birds that fly into oil pits, mining sites, telecommunications towers, wind turbines and other hazards should be treated as accidents not subject to prosecution. And an Interior Department proposal would cement that into federal regulation.

State officials and wildlife advocates who are suing the administration in federal court say birds already are being harmed under actions allowed by a 2017 Trump administration legal memo that signaled the rule change.

Most notable was the destruction last fall of nesting grounds for 25,000 shorebirds in Virginia to make way for a road and tunnel project. State officials had ended conservation measures for the birds after federal officials advised such measures were voluntary under the new interpretation of the law.

The move to relax the bird law, combined with Trump rollbacks of the Endangered Species Act and the National Environmental Policy Act puts birds and their habitat at greater risk, said Audubon Society vice president Sarah Greenberger.

The Trump administration proposal follows longstanding pressure from oil companies, utilities and other industries.

The Edison Electric Institute, which represents many U.S. utilities, contends it would be “absurd” to criminalize “ordinary, everyday activities” that happen to result in a bird death, which can result in up to six months in prison and a $15,000 penalty for every bird injured or killed.

The American Petroleum Institute suggested in a regulatory filing that “The birds themselves are the actors, colliding or otherwise interacting with industrial structures.”

More than 1,000 types of birds are covered by the law, from water birds such as ducks and pelicans, to woodpeckers, songbirds, hawks and owls.

Criminal enforcement of the law typically was used only as a last resort, according to current and former U.S. Fish and Wildlife Service officials.

The agency conducted 152 investigations into bird deaths across the U.S. over a five-year period ending Dec. 31. 2017, according to spokesman Gavin Shire. Most involved birds killed by power lines, which kill upward of 25 million birds annually, according to a 2014 government-sponsored study.

The number of investigations resulting in prosecutions was not available, Shire said.

“The goal was to generate voluntary compliance. You do that by educating people,” said Gary Mowad, who served as deputy chief of enforcement during a 25-year-career with the agency. “We did a great job of keeping (bird) mortality in control. The only regulatory tool that the federal government had at its disposal to address that is now gone or will be gone.”

The most notable enforcement case bought under the migratory bird act resulted in a $100 million settlement by BP, after the Gulf of Mexico oil spill in 2010 killed approximately 100,000 birds.

Federal courts have been split on whether companies can be prosecuted, with appeals courts ruling in favor of industry three times and siding against companies twice.

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At the Berkeley Pit, initial efforts to discourage birds from landing were prompted by deaths of 342 snow geese that landed in November, 1995.

Over the next two decades, an average of six birds per year were found dead in the pit, Thompson said.

“We quickly learned that warning shots from a high-powered rifle worked great and that pretty much carried us through ’til 2016,” he said.

Then in November 2016 a huge, exhausted flock of snow geese that stayed at their summer grounds in Canada longer than unusual were forced quickly south by cold weather. They found the Berkeley Pit to be the only open water to escape a sudden snowstorm — and an estimated 3,000 to 4,000 of the birds that landed there died.

In response, Montana Resources dramatically ramped up its bird scare tactics and Thompson said it would keep up the efforts regardless of the Trump administration’s actions, mirroring pledges from some other companies and industries.

Much of the attention over accidental bird deaths has focused on oil companies.

Kathleen Sgamma, president of the industry group Western Energy Alliance, said that estimates of as many as a million birds killed annually in oil pits are outdated because companies have shifted away from using open pits to store hazardous waste from drilling.

“The studies haven’t caught up with the realities on the ground,” Sgamma said.

The U.S. Fish and Wildlife Service disputed Ashe’s claim that billions more birds were at risk from the rule change and noted that most preventive measures already are voluntary ones.

“Without a scientific basis, any claim as to the number of birds that would be negatively affected would be speculative and irresponsible,” Shire said in an emailed statement.

Ashe’s estimate that billions of birds were at risk was supported by a leading ornithologist from Cornell University and two former senior officials with the Fish and Wildlife Service — Brad Bortner, who retired in 2017 from his post as chief of the migratory bird program, and Paul Schmidt, the agency’s former assistant director.

“If we’re talking about over decades, and a billion birds already are killed by industry annually, that does start really adding up pretty quickly,” said Amanda Rodewald, co-director of Cornell’s Center for Avian Population Studies. “We’re talking about a scale of mortality that’s substantial, that would be meaningful ecologically and biologically.”