Contaminated water kills thousands of Snow Geese in Montana

Several thousand Snow Geese have died a harrowing death after a blizzard forced large flocks to land on the acidic, metal-laden waters of an old open-cast mine in Montana on the night of 28 November.

The death toll at Berkeley Pit near Butte has been estimated from drone and aircraft flights over the pit. The exact number of dead geese is yet to be confirmed, but the mining company Montana Resources expects the total to be many times more than the 342 that died at the same pit in 1995.

Though it was estimated that 90 per cent of the massive flock, suspected to exceed 10,000 individuals, was chased off the pit by 29 November, that did not necessarily save them. Because exposure to the pit water does not mean instantaneous death, it is entirely possible that the toll will continue to rise in the coming days. The Montana Standard has reported that Butte residents have found dead birds in a Walmart parking lot, on roadsides and outside the city since the episode.

The water in Berkeley Pit is considered acidic enough to liquefy a motorboat's steel propeller. Post-mortems conducted on some of the 1995 victims found that the oral cavity, trachea, and oesophagus, as well as digestive organs like the gizzard and intestines, were lined with burns and festering sores, thus causing a painful death. The US Fish and Wildlife Service picked up 23 dead Snow Geese from the site on Wednesday; these will be sent to a lab for necropsies.

Such a high number of Snow Geese in the Butte area is exceptional, with between 2,000 and 5,000 birds usually noted on both spring and autumn migration. Mark Thompson, environmental affairs manager for mine company Montana Resources, said: "I can't underscore enough how many birds were in the Butte area that night...numbers beyond anything we've ever experienced in our 21 years of monitoring by several orders of magnitude."

Snow Goose (Photo: Tom Ingram)

The world population of Snow Goose has increased greatly in recent decades. Estimated at three million individuals 30 years ago, the current population is thought closer to 15 million. Birds are increasingly seen in areas where they were historically scarce as they search for suitable wintering areas.

The 1995 incident prompted a mitigation effort that seeks to protect birds from the toxic water. This included an observation deck, with telescopes and spotlights, from which spotters could scan for incoming geese. If a flock was seen approaching, employees typically fire off shotguns or loud rifles to deter the animals from coming closer. Devices known as 'Phoenix Wailers' (speakers that emit loud electronic noises and predator cries) are also sited around the pit. Until 28 November, this had been working well — for example, just 14 bird fatalities were logged at the site from 2010–2013.

Mountana Resources, along with Atlantic Richfield, could be fined if it is determined that the companies were not in compliance with the bird-scaring programme, but Mr Thompson said he was confident the efforts were adequate.