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In late October, while much of the country was engrossed with the Paul Manafort indictment and Halloween plans, Stella Capoccia was fixated on the number of migrating Snow and Ross’s Geese piling up on the Canadian border. From her base in Butte, Montana, she checked in daily with biologists and naturalists in Canada and Montana, scoured eBird for new reports, and combed through Facebook birding pages for the latest sightings of the garrulous waterfowl, collectively called white geese. The number of birds grew from the thousands, to the tens of thousands, to more than 100,000 by November 2, when a snowstorm spurred them south. Capoccia raised the alarm: The white geese were coming.

The previous fall several thousand white geese died when they landed amid a fierce storm on the Berkeley Pit, a former open-pit copper mine on the edge of Butte now designated as part of a site. Capoccia, a biology professor at , heads an advisory board created last year to devise protocol to prevent birds from landing in the 400-acre pool, where they can die by��drinking the��poisonous water. The group, which includes��state wildlife biologists, a renowned white goose expert, and Montana ̽����ѡ staff,��is aiming for military precision: Ideally the communication network will alert the advisory board when a potential situation is developing, and they, in turn, will notify mine employees to watch for incoming birds and ready their arsenal of non-lethal devices to drive them away. Nobody—not the companies in charge of the site, the state and federal agencies that oversee wildlife and the cleanup of the area, or the public—wants a repeat of last year’s ghastly incident.

In a haunting echo of that event,��this November 4 the cacophony of tens of thousands of white geese flying overhead filled Butte like the earsplitting chatter at an overcrowded bar.��This time, however, mine employees were primed for their arrival, thanks to the fledgling warning system devised by the advisory board. They worked 24/7 for four days employing a variety of new tools, including a handheld laser��and a massive machine that blasts air at 200 miles per hour, to scare off 600 geese. Not a single animal died.

“They were able to respond with the appropriate hazing levels and the appropriate technology,” Capoccia says of the mine company Montana Resources, which, along with the company Atlantic Richfield Corporation, is responsible for the Berkeley Pit Superfund site. She credits both companies for stepping up their efforts to avian deterrent and hazing efforts. They have poured $500,000��into the program this year, and miners have dedicated countless hours to avian identification and monitoring. “We’re just a lot better prepared,” says Mark Thompson, MR environmental affairs manager, recalling last year’s mortalities. “It was traumatic for everybody involved. When you see animals suffering and you’re powerless to do anything about it, it’s not a good situation.”

There are, of course, factors beyond the emotional toll. MR potentially faces hefty fines for violating the Migratory Bird Treaty Act; the EPA is still reviewing the incident and hasn’t yet made a decision. And, simply put, thousands of birds being poisoned to death is just really bad PR.

“If it weren’t for the fact that the pit is in Butte, almost nobody would care,” says Brent Lonner, the wildlife biologist in charge of the , a rural white-goose stopover 160 miles north of Butte. “But thousands of geese died right in town.”

While hazing efforts this fall have been overwhelmingly successful so far, the advisory board and MR realize that there’s still much to figure out when it comes to preventing avian deaths. And with the increased scrutiny and concern after last year’s die-off, it’s become apparent that Snow Geese aren’t the only birds at risk. Dozens of migrating waterfowl species are drawn to the dangerous waters.

A Deadly Stopover

The Berkeley Pit opened in 1955, and by the time Atlantic Richfield suspended operations in 1982, some had been mined. When mining ceased, the company shut down the underground pumps that prevented groundwater from flooding the shafts and tunnels. The��water immediately began filling the estimated of subsurface passageways beneath Butte and spilling into the mile-by-mile-and-a-half pit. Today, the acidic lake is roughly 1,060 feet deep. (For reference, Idaho’s Lake Pend Oreille, where the Navy tests submarines, extends down .) Since MR has mined and processed copper and molybdenum at the site.

White geese do not usually��stop in Butte. The Arctic breeders—up to one-third of the total population—typically leave their stopover site in Canada in late October and fly 600 miles to Freezout Lake. They refuel for a few days in surrounding barley fields, then trace the eastern slopes of the Rockies, cross the Continental Divide, and wing it southwest to their wintering grounds in southern Oregon or California’s Central Valley. Instinct compels them to race ahead of storms or follow behind them. But if they get tangled in inclement weather along the Rockies and the stars by��which they navigate are obscured, they can be funneled to Butte, where the floodlit pit inadvertently acts like a beacon, luring the exhausted, dehydrated birds to a large expanse of water that hasn’t frozen over since the early 2000s.��

The pit’s potential as an avian deathtrap came to light in November 1995, when 342 Snow Geese caught in a storm perished in the metal-laden lake. The loss of so many pristine birds on a water body they couldn’t distinguish as polluted made national headlines. After that incident, state and federal agencies worked with MR and Atlantic Richfield to design a hazing program. It largely consisted of mine employees scanning the pit every hour for birds, deploying noisemakers like Phoenix wailers—they blast avian alarm calls and industrial noises every three minutes or so—to prevent birds from landing, and popping off shots with a rifle to spur them to leave when then did. For two decades, it worked. From 1996 through the summer of 2016, an estimated 96,000 birds of various species were observed in or around the pit, and there were fewer than 200 documented mortalities.

Then, in the fall of 2016, almost 21 years to the day after the first mass incident, the geese returned—and in far greater numbers. Mild weather and grain-rich fields had lulled white geese into staying north a couple of weeks longer than they usually do. On the evening of November 28, in a mad rush to stay ahead of a winter storm, thousands of geese flew over Freezout Lake, which had frozen over. They beat past another occasional stopover 20 miles north of Butte, Warm Springs Ponds, whose waters were also ice. Then they hit Butte, their shrill, urgent calls piercing the night air as they circled in search of a place to set down. “The noise was deafening,” Thompson recalls. The next morning, mine employees saw a staggering sight: at least 10,000, perhaps as many as 60,000, geese in the pit. Mine employees worked tirelessly for 10 days to move the birds off the water, adding pyrotechnics to their existing suite of tools. They dispersed most of the geese, but an estimated 3,000 to 4,000 died on the water.

It isn’t simply the acidity of the lake, which at 3.7 is roughly equal to , that makes the water so deadly. The dissolved metals, especially copper and zinc, can exacerbate the corrosiveness of acidic water, according to the pathology report on Snow Geese that died in the pit last year. Necropsies at the USGS National Wildlife Health Center showed that geese had elevated levels of manganese, zinc, copper, iron, and cadmium in their livers and kidneys. As the parched birds sucked down the caustic brew, lesions formed in their throats, stomachs, and intestines, and the metal overload may have caused kidney failure. (If a person fell into the pit, the immediate threat would likely be hypothermia: The water is 55 degrees at the surface and plummets quickly, hitting 36.5 degrees 50 feet down.)

“For two decades we were exceptionally effective,” Thompson says. “But we’d never had 10,000 birds land at once. We need to know what potential factors that lead to this kind of situation. And we’re going to find out how unpleasant we can make a single location.”

Next time, he wants to be prepared.

Aware and Prepared

On a sunny, crisp morning in late September, Mike Schwitters drove slowly around the lake and six ponds that make up the Freezout Lake WMA. Creeping along the dirt roads, he’d wave to the occasional orange-vested hunter who was likely after the same quarry as him: white geese. Every day for nearly 30 years during spring and fall migration Schwitters has surveyed waterfowl here. A retired Air Force officer and meteorologist, the amiable septuagenarian has embarked on a second career as a white goose expert who, in addition to his work at Freezout, has chased the birds throughout their Arctic breeding grounds. He can recognize individual birds amid a thousands-strong flock by their unique neckbands.

“I think Mike will be reincarnated as a Snow Goose,” Capoccia jokes.

Schwitters’s expertise was what Capoccia looked for when pulling together the advisory board. He’s an invaluable link in the extensive communication network of biologists, naturalists, and climatologists that extends from Alberta to Utah and helps determine when birds might be on their way to the pit. On that September morning, Schwitters emailed the advisory board the tally of 260 white geese. It was lower than he’d expect at that point in the migration season, likely due to warm conditions up north; as climate change causes fall temperatures to , it might increasingly mess with the cues that trigger the birds to move to wintering grounds. No reason, then, to up the newly instituted hazing level at the pit from standard to heightened or urgent.��

The warning system is one critical part of the program; preparedness at the pit is another. Bird guide Gary Swant has lead an avian ID training program for pit employees that focuses on the 42 species likeliest to land there. White geese, which are strong in the Pacific Flyway, represent the largest volume of birds ever seen on the pit, but plenty of other waterfowl land on the poisonous waters—as happened in late September, when 1,200 American Coots, Eared and Western Grebes, Gadwalls, American Wigeons, Mallards, Redheads, and Ruddy Ducks set down. Identifying which species they’re dealing with and noting how certain ones react to each tool could ultimately help devise species-specific approaches. While the primary goal is keeping birds off the pit, hazing a night-migrating, diving duck throughout the day, for example, will just exhaust the animal, forcing it to plummet repeatedly and further exposing it to the toxin-laden water. ��

At first Swant questioned how seriously employees would take the lessons, given that “they’re miners first.” Their commitment, even enthusiasm, quickly dispelled his doubts. “We’re giving them every advantage we can think of to turn them into junior field biologists, and they’re accepting the challenge.”

The advisory board considered roughly two dozen deterrents and hazing techniques. “We became a sort of��‘no’ group—why this isn’t going to work,” Capoccia says.

Simply draining the pit of its 46.8 billion gallons of water, for example, isn’t an option. The liquid is toxic, and a federally approved plan already exists to address the rising water level; spill in from what Thompson calls the “rat maze” of passageways under the town. Models project the water will reach a critical level in 2023, potentially seeping into��shallow aquifers that��ultimately feed local waterways;��a treatment plant is slated to discharge 7 millions gallons per day, up from 5��million now, in order to keep the water in check. A suggestion to cover the surface with plastic balls like the ones that blanket a Los Angeles reservoir was nixed for two reasons: They’d impede evaporation on the ever-growing lake, and so many would be required that the company would have to build a new factory in Butte, which would take years and millions of dollars. The idea of suspending cables above the surface was intriguing, but the realities of anchoring the colossal system to the unstable pit walls killed the notion. (A landslide in 1996 caused a 50-foot tidal wave to surge across the water, and after a smaller collapse in 2012 MR banned humans from the water—a prohibition that made hazing geese in 2016 that much trickier.)

The group also had to consider which gadgets could function in the driving snow, whipping winds, and sub-zero temperatures that coincided with last year’s big mortality event.

So far, the advisory board has recommended testing a handful of devices, ranging from a $100 fixed-wing mini drone painted to look like an eagle to the Vortex Ring Accelerator Deterrent (), an air cannon that costs hundreds of thousands of dollars. The VRAD was originally designed to disperse hail clouds over crops,��but operators noticed that it also had the unexpected perk of causing birds to flee.

Testing, Testing

In late November, MR set up all of the new devices near the edge of the pit by the Bird Shack, the former truck control center that now serves as the avian monitoring station. It’s outfitted with high-powered binoculars and a scope, a binder for recording bird sightings during the hourly surveys, a poster with the 42 birds, hazing guidelines, and safety protocols. (Do not, for instance, operate the laser from 6-6:45 a.m. or 11 p.m. to midnight in order to avoid accidentally temporarily blinding a pilot flying a commercial plane to or from the municipal airport.)

There was a science fair-like atmosphere, with each gadget introduced in turn and briefly demonstrated. Jim Jonas, a pilot who enjoys soaring in a sailplane amid Golden Eagles and Osprey as they migrate over the Bridger Mountains, sent the raptor-size fixed-wing plane swooping over the water. “We want to enhance the color: white body, dark head, light tail,” Swant said. “Bald Eagles have come into the pit and taken coots.”

As if on cue, a real baldy glided past, cocking its head to eye the ersatz raptor.

A more traditional-looking drone, a multi-copter, has been souped-up with flashing lights, a siren, and the ability to carry a payload of water balloons to drop on sitting ducks. “Could you possibly find that merganser for us?" Swant asked, referring to the lone bird paddling around the lake. To everyone’s disappointment it had swum directly below us, out of view.

Another tool, a laser, emitted a green beam strong enough to reach the far wall a mile away; nobody knows exactly why lasers cause birds to disperse, but they’re being investigated to repel avian species from crops, landfills, and airports.

Everyone inserted earplugs while the VRAD warmed up; , an environmental consultant, leaned over and suggested I pull them out as soon as I felt the bone-shattering “BOOM!” I did, and heard the whistle of air move across the water and hit the far wall.

A custom-built, gas-powered air-boat drone that might flush birds from the surface stayed on dry ground, as it won’t be ready to launch until later this month. About the size of a Radio Flyer wagon, it was constructed with the pit conditions in mind: The hull is carbon fiber, the electronic components are housed in waterproof casings covered in a corrosion-resistant spray, and it has the ability to carry 20 pounds—a feature that could come in handy to haul more deterrents out onto the water.

While everyone stresses that they’re still figuring out the best uses for the various devices, clues are emerging. The laser was key in the departure of hundreds of coots in September. They didn’t get the chance to see what effect the hawk drone might’ve had on those 1,200 birds—as soon as it went up, it sent back a “batteries are cold” signal, so it had to come right back down. When the Snow Geese moved through in early November, a shot with the VRAD caused only two to take flight. They’re meticulously compiling those findings, as well as which build-ups of various avian species 20, 50, or hundreds of miles away—and under which conditions—reach the pit.��

Since the calamity last fall, MR has recorded 5,000 birds on or above the pit, and nine mortalities (a Western Grebe and eight white geese)—a rate comparable to that seen during the two decades between die-offs.

“One year’s data is not going to prove anything,” says Swant, who notes that conditions were far milder this year when geese moved through: 13 degrees warmer and clear skies, likely allowing most birds to make a straight shot for their wintering grounds. “But over time I think we’re going to see less birds on the pit and for shorter periods of time, and we’re going see birds not land because of the hazing protocols we’re putting in place.”

Looking Ahead

In the meantime, the advisory board still has plenty of challenges to grapple with. What should be done with injured birds? Four Snow Geese pulled from the pit this fall were rushed to a vet to have their gastrointestinal systems flushed; all recovered and were released within a day or two, and MR and ARCO picked up the tab for the rehab. But what if birds take longer to recover and miss the migratory window? Another uncertainty is whether to deploy three dozen Snow Goose decoys on a clean tailings pond two miles north of the pit during a heightened white-goose watch; the board hasn’t determined whether it’s worth encouraging the birds to land anywhere in the pit’s vicinity.��And then there’s the question of lights: Illumination in the area near the pit at night may attract and disorient migrating birds, as happens with skyscrapers in cities. Might a����help?

While their focus is protecting birds at the pit, the knowledge they’re gaining about avian behavior could have applications far beyond Butte.

“One of the thoughts I had coming onto this advisory council is that the Berkeley Pit is not the only toxic place waterfowl hit on their migratory route,” says Amy Seaman, a employee who previously worked on a hazing program at a lithium mine in Nevada. She points to the Athabasca Tar Sands and Mount Polley tailings pond in Canada, cyanide leach-pits across the United States, evaporation pond systems at Utah potash mines, and a series of copper mines in Southern Arizona, just to name a few. “Birds are encountering a lot of these places along the way, so there are potentially a lot of other sites that could learn from what’s happening at the Berkeley Pit.”

For now, however, the primary focus is analyzing the performance of the tools during fall migraiton, which ended December 15, and��gearing up for spring. Whenever the next group of birds appears over the steep, tiered walls of the pit and makes for its rust-hued water, the lasers will light up, the VRAD will roar to life, the drone will lift off, and the grand effort to save birds from the inadvertent death trap perched high in the Rockies will continue.��

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Correction: This article has been updated to clarify the extent��of the pit water and��the level of lighting around the site.