2011 began with a series of high-profile bird disasters, and now a new one has struck as the year comes to an end. Nearly 12 months after thousands of crows and blackbirds mysteriously died from Arkansas to Sweden, an estimated 1,500 eared grebes — a duck-like aquatic bird — have fallen to their deaths in southern Utah.

The migratory birds crashed into a Walmart parking lot, football fields and various other snow-covered surfaces, which they apparently mistook for bodies of water, according to reports in the St. George Spectrum and the Associated Press. Volunteers have rescued at least 3,000 injured grebes between St. George and Cedar City, Utah, while officials say more than 1,500 may have been killed.

"They're just everywhere," state wildlife official Teresa Griffin tells the Spectrum. "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."

The grebes were most likely migrating toward Mexico for the winter, Griffin says, when they saw what seemed to be unfrozen ponds and lakes where they could rest. Failing to realize the surfaces were actually solid ground, the birds then plummeted downward in a mass accidental suicide.

Such bird die-offs aren't uncommon, as many experts explained earlier this year when thousands of red-winged blackbirds died in Arkansas, 500 more died in Louisiana, and up to 100 crows died in Sweden. But they are usually caused by a combination of factors, often including human activity. The Arkansas blackbird deaths were blamed on New Year's Eve fireworks, for example, which presumably scared and disoriented them until many of the birds suffered fatal crashes.

In the case of the Utah grebes, wildlife officials say the problem was probably a combination of stormy weather and artificial lights — such as those adorning most Walmart parking lots. "The storm clouds over the top of the city lights made it look like a nice, flat body of water," Griffin tells the Spectrum. "All the conditions were right."

As another bird expert points out to the AP, bright lights on the ground often disorient migratory birds like grebes, which navigate by starlight at night. "Before there were [artificial lights], the sky was always paler than the ground," says Kevin McGowan, a behavioral ecologist at Cornell University's Lab of Ornithology. "When all of a sudden there's light all over the place, they don't know which way is up anymore."

Mass death events are typically defined as those in which more than 1,000 birds die, and the National Wildlife Health Center has received more than 175 reports of such events in the past decade. The triggers vary from disease and weather to trauma and starvation, but Griffin says this week's event stands out because it covered such a large area, up to 30 miles across. "I've been here 15 years, and this was the worst downing I've seen," she says.

On the bright side, the Utah Division of Wildlife Resources has been taking the injured grebes to nearby lakes and ponds, where they can recover from their injuries without needing to fly. According to an agency spokesman, "The likelihood is that most of them will survive."

Here's a video of volunteers releasing the grebes into Utah's Quail Lake on Tuesday:

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Mass bird deaths bookend 2011
Nearly 12 months after a rash of bird bloodbaths made international news, another big avian 'Aflockalypse' has struck in southern Utah.