Thousands of migratory birds died on impact after apparently mistaking a Wal-Mart car park and other areas for bodies of water and plummeting to the ground.
Crews went to work cleaning up the dead birds and rescuing the survivors after the creatures crash-landed in St. George, Utah, in what one wildlife expert called the worst downing she's ever seen.
The crash happened on Monday night and by midday Wednesday, volunteers had helped rescue more than 3,000 birds, releasing them into nearby bodies of water.
'They're just everywhere,’ said Utah Division of Wildlife Resource spokesman Teresa Griffin.
‘It's been non-stop. All our employees are driving around picking them up, and we've got so many people coming to our office and dropping them off.’
Stormy conditions probably confused the flock of grebes, a duck-like aquatic bird likely making its way to Mexico for the winter, which tried to land in a Cedar City Wal-Mart car park and elsewhere.
The birds plunged into the car park, football fields, highways and over miles of property that had been blanketed by about three inches of gleaming snow. At least 1,500 are believed to have died.
‘The storm clouds over the top of the city lights made it look like a nice, flat body of water. All the conditions were right,’ Ms Griffin told The Spectrum newspaper in St. George.
‘So the birds landed to rest, but ended up slamming into the pavement.’ No human injuries or property damage have been reported.
Kevin McGowan, who studies birds at the Cornell Lab of Ornithology in Ithaca, New York, said grebes rely on starlight to navigate during their nighttime migration.
'Before there were (artificial lights), the sky was always paler than the ground,' he said. 'When all of a sudden there's light all over the place, they don't know which way is up anymore.'
It's not uncommon for birds to mistake hard surfaces for water. However, Ms Griffin noted most downing cases are localised, while ‘this was very widespread’.
‘I've been here 15 years and this was the worst downing I've seen,’ she said.
Wildlife officials said they were continuing the rescue effort that started on Tuesday afternoon and included an enthusiastic group of volunteers.
‘I have never in my life encountered such a thing,’ Stephen Gwin told The Spectrum.
‘I've heard of fish die-offs and other strange natural phenomenon, but I've never experienced one before.’
Mr Gwin has an environmental biology degree and added: ‘It was very strange, but very fun.’
The surviving grebes were gathered up - some in cardboard boxes - and dropped into bodies of water in southern Utah's Washington County, including a pond near Hurricane.
Residents who came across remaining grebes were asked to either call wildlife officials or bring the birds to their office.
‘If we can put them on a body of water that's not frozen over, they'll have a better chance of survival,’ said wildlife agency spokesman Lynn Chamberlain.