Several thousand snow geese died after a snowstorm forced tens of thousands of the migratory birds to take refuge in the acidic, metal-laden waters of an old open pit mine in Montana last week.
But the toll could have been much worse, said Mark Thompson, environmental affairs manager for mine company Montana Resources. Along with the Atlantic Richfield Co, Montana Resources is responsible for Berkeley Pit, a Superfund site in Butte.
Witnesses said the pit looked like "700 acres of white birds," on November 28, Thompson said Tuesday.
Since then, employees of MR and Arco have used spotlights, noise makers and other efforts to haze the birds off the water and try to prevent others from landing.
The companies estimate that over 90 percent of the birds were chased off by the morning of November 29, Thompson said.
Workers received some advance notice about the incoming flock from an off-duty Montana Resources employee about 25 miles away, who called to report there were about 25,000 geese in the air in Anaconda, Thompson said.
"I can't underscore enough how many birds were in the Butte area that night," Thompson said. "Numbers beyond anything we've ever experienced in our 21 years of monitoring by several orders of magnitude."
The employees "did incredible things to save a lot of birds and they really put their heart and soul behind it," he said. "They did everything they could think of."
Typically, Butte sees between 2,000 and 5,000 birds all year, including spring and water migration, Thompson said. The estimated death toll is based on drone and aircraft flights over the pit, which holds about 45 billion gallons of water.
Thompson said federal and state agencies are still confirming the number of dead geese.
Nonetheless, the company expects the total will be many times more than the 342 that died in 1995, prompting the creation of the mitigation effort that seeks to protect birds from the toxic water.
"Some of the things that MR and Arco experimented with this time were successful," Thompson said, and may be adopted into the mitigation plan if they're approved by the Environmental Protection Agency.
The companies are looking at incorporating emerging technologies, such as drones, he said.
The companies are going to investigate to try and determine what circumstances led to "this kind of perfect storm," with thousands of birds making a late migration and then facing a snowstorm at a time that Berkeley Pit had the only open water in the area.
University of Montana Western professor Jack Kirkley, who specialises in ornithology, told The Montana Standard that recent milder winters aren't encouraging birds to head south as early and in some cases, are causing some to stay in places where they've never stayed the winter before.
He notes that there are 4 million to 6 million snow geese on the continent, and there are some concerns that the population is too high.
MR and Arco could be fined if the EPA determines the companies were not in compliance with the bird hazing program, but Thompson said he is confident the efforts were adequate.