Thousands of migratory birds were killed or injured after apparently mistaking a Wal-Mart parking lot, football fields and other snow-covered areas of southern Utah for bodies of water and plummeting to the ground in what one state wildlife expert called the worst mass bird crash she'd ever seen.

Crews went to work cleaning up the dead birds and rescuing the injured survivors after the creatures crash-landed in the St. George area Monday night.

By midday Wednesday, volunteers had helped rescue more than 3,000 birds, releasing them into a nearby pond. There's no count on how many died, although officials estimate it's upwards of 1,500.

"They're just everywhere," said Teresa Griffin, wildlife program manager for the Utah Division of Wildlife Resource's southern region. "It's been nonstop. All our employees are driving around picking them up, and we've got so many people coming to our office and dropping them off."

No human injuries or property damage have been reported.

Officials say stormy conditions probably confused the flock of eared grebes, a duck-like aquatic bird likely making its way to the Mexican coast for the winter.

The birds plunged into a Cedar City Wal-Mart parking lot, football fields, highways and over miles of property that had been blanketed by about 3 inches of gleaming snow.  The rescue effort that started Tuesday afternoon included residents collecting grebes -- which weigh about a pound -- and delivering them in cardboard boxes to the wildlife department's office.

Officers said once they dropped the birds into bodies of water in southern Utah's Washington County, including a pond near Hurricane, the water-loving creatures were "very active."

Many of the birds had broken wings or other injuries from the accident. Wildlife agency spokesman Lynn Chamberlain said the birds' hollow bones can heal, although humans can't do much to help the process.

Keeping them in water -- where they have food and won't have to fly -- improves their chances.

"We're giving them the best shot they can," Chamberlain said. "The likelihood is that most of them will survive."