Motorists stopped and gawked at hundreds of dead red-winged blackbirds on a highway in Pointe Coupee Parish, La., Monday, just days after residents of Beebe, Ark., saw more than 1,000 birds fall from the sky on New Year's Eve.

On Monday, state biologists were gathering up some of the approximately 500 blackbirds and starlings that lay dead along Louisiana Route 1 near Pointe Coupee Central High School for testing.

The United States Geological Survey has noted 16 incidents in the past 30 years where more than 1,000 black birds have died at the same time, usually the result of tightly-packed flocks flying into bad weather. What's more, more than 5 billion birds die of natural causes in the United States each year, so it is, in a way, unusual that Americans don't witness more major bird kills.

Yet the use of improved testing and a state of heightened concern on the parts of state ornithologists is a proper response, even if the two bird kills had not come so close together, experts say.

"Birds can be really good indicators of environmental problems, so I'd hate to think that 5,000 would die and nobody would care," says Greg Butcher, director of bird conservation at the National Audobon Society, in Washington. "It's worth investigation to find out what happened because there is potentially something we should worry about and it's potentially something that has an odd, but benign cause."

Americans have theorized that everything from fallout from secret government weapons testing to UFO collisions downed the birds in Arkansas. But the newly-discovered bird rain in Louisiana is likely to focus more serious attention to the plight of blackbirds now bundled in winter flocks that can number over 100,000 birds.

Postmortem tests of birds in the Arkansas incident showed evidence of blunt force trauma to many of the victims, which Mr. Butcher says means that it's likely the birds were spooked by New Year's Eve fireworks and may, in mass confusion, have run into cars and houses.

Since blackbirds are considered a nuisance by farmers, the mass death in Louisiana could be attributable to a legal pest control effort. Pest control experts kill blackbird roosts in several ways, including spraying water on birds to induce hypothermia or by using legal poisons. Most such poisons work quickly, but a botched control attempt could mean that birds may have flown away from the roost and died nearby.