On New Year's Eve thousands of red wing black birds showered a neighborhood in the small town of Bebee, AK. Wildlife officials investigating the massive bird kill believe fireworks may have startled the roosting birds and caused them to crash into power lines, trees and houses. The fireworks may have been what got them up in the air in the first place at night when they are not supposed to be flying around, but that doesn't fully explain what happened.

There are many different reasons for mass bird kills -- poisoning, a strange weather event attributed to climate change, or pollution.

Some say we are at a tipping point in the ecology of our environment. Many prophets and ancient civilizations have predicted times in the future of famine, drought, climate change, and death. Some say we may be close to that tipping point in which the entire system may come crashing before our very eyes.

The lead detective in the case of the raining birds loaded her car with boxes of the dead creatures on Monday, taking them for shipment to a national laboratory in the hope that tests would reveal why thousands of birds suddenly fell from the sky upon the small town of Beebe, Arkansas.

Early tests on the birds showed no toxic gases trapped in their feathers, though biologists found some physical trauma indicative of being hit by hail or lightning. Still, a bird die-off of this magnitude is unusual.

Beebe's blackbird population is large enough so that the US Department of Agriculture has in the past attempted large-scale scarecrow techniques to move large flocks out of the area. Outnumbered and outmaneuvered, the USDA gave up those efforts a few years ago.

In 1973, several hundred ducks dropped from the sky near Stuttgart, Ark., known as "The Duck Capital of the World," victims of a sudden storm. In another case, biologists found hundreds of what Ms. Rowe calls "perfectly good," but dead, pelicans in the middle of the woods. While the pelicans showed no outward signs of injury or singe marks, necropsies showed they'd been hit by lightning.

It's the stuff of apocalyptic novels. Scientists have not yet ruled out pollution or chemical toxins as the cause of nearly a dozen mass animal die-offs, from Arkansas to Brazil, in the last week. But as officials investigate, both the mundane and the intriguing are emerging as potential causes.

Because birds are considered indicator species that reflect the health of the surrounding environment, the news of mass deaths has unsettled many Americans.

Mass bird kills aren't uncommon. The US Geological Survey documented 90 mass deaths of birds from June to December last year. Over the past 30 years, it counts 16 events in which 1,000 birds or more suddenly died.

Testing can take time and is often inconclusive, although methods have improved in recent years, says Greg Butcher, a conservationist at the National Audubon Society. Scientists hope to have an explanation for the Arkansas bird kill within three weeks.

Nevertheless, officials in Arkansas and Louisiana call the large number of bird deaths "unusual." While the ultimate explanations may not point to broader environmental problems, "it is something we should potentially worry about," says Mr. Butcher at the National Audubon Society.