NEW ORLEANS — Some 500 dead and dying birds fell onto a Louisiana highway on Monday, just three days after a similar incident in Arkansas.
The events have led to speculation running from poisonings to "End of Days" scenarios, but a key federal agency emphasized that mass bird die-offs are not that rare.
Most of the birds found on Louisiana Highway 1 near Point Coupee were red-winged blackbirds, as was the case in Beebe, Ark., some 360 miles away. The species is one of the most common in the United States, with a population estimated at up to 200 million.
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Some of the Louisiana birds will be tested by the National Wildlife Health Center run by the U.S. Geological Survey. But a USGS spokesman told The Baton Rouge Advocate that USGS records showed 16 incidents in the last 30 years where more than 1,000 blackbirds have died all at once.
"These large events do take place," he said. "It's not terribly unusual."
The National Audubon Society agreed that mass bird die-offs are not rare. "Initial findings indicate that these are isolated incidents," Greg Butcher, Audubon's director of bird conservation, said in a statement.
The Louisiana Department of Wildlife and Fisheries also weighed in, saying that necropsies on some birds indicated many "exhibited traumatic injuries." The birds might have flown into nearby power lines, it added.
Two dozen of them had head, neck, beak or back injuries.
About 50 dead birds were near a power line 30 or 40 feet from Louisiana Highway 1. About a quarter-mile away, a second group of 400 or more stretched from the power line and across the highway.
Dan Cristol, a biology professor and co-founder of the Institute for Integrative Bird Behavior Studies at the College of William & Mary, said the Louisiana birds might have been ill or startled from their roost, then hit the power line.
"They don't hit a power line for no reason," he said.
In Arkansas, preliminary tests showed the blackbirds there, as many as 5,000, died after massive trauma. Experts said the birds were likely spooked by fireworks, lightning or some other loud event and then ran into each other and other objects as they fled at night while roosting.
"The birds suffered from acute physical trauma leading to internal hemorrhage and death," the Arkansas Game and Fish Commission said in a statement Monday. "There was no sign of chronic or infectious disease."
The birds were otherwise healthy, according to the statement.
The injuries were primarily in the breast tissue, with blood clotting and bleeding in the body cavities.Story: No poison found in birds that fell on town
Dr. George Badley, the state's top veterinarian, told NBC News that the birds died in midair, not on impact with the ground.
That evidence, and the fact that the blackbirds fly in close flocks, suggests they suffered some massive midair collision, he added. That lends weight to conclusion that they were startled by something.
Fireworks that night might have frightened the birds into such a frenzy that they crashed into homes, cars and each other. Some may have flown straight into the ground.
"It was New Year's Eve night. Everybody and their brother was shooting fireworks," said Beebe Police Chief Wayne Ballew. The city allows fireworks only on New Year's Eve and Independence Day.
The commission noted that "loud noises were reported shortly before the birds began to fall from the sky," adding that blackbirds seldom fly at night.
"The blackbirds were flying at rooftop level instead of treetop level" to avoid explosions above, according to Karen Rowe, an ornithologist with the commission. "Blackbirds have poor eyesight, and they started colliding with things."
Another theory was that severe weather such as lightning accounted for the loud noises but this was discounted because the violent weather had already left the area.
The commission also is trying to determine what caused the deaths of up to 100,000 fish over a 20-mile stretch of the Arkansas River near a dam in Ozark , 125 miles west of Beebe. The fish were discovered on Dec. 30.Video: Arkansas’ animal deaths: Coincidence or conspiracy?
The commission expects results on the fish tests in probably a month. Disease may be the culprit, since almost all the fish were one species — bottom-feeding drum, the commission said.
Keith Stephens, a commission spokesman, said the events do not appear to be related. Both that section of the river and the air at the site of the bird deaths were tested for toxins, Stephens said.
Residents of Beebe, a community of 5,000 northeast of Little Rock, told how dead birds ended up"littering the streets, the yards, the driveways, everywhere."Video: Arkansas resident: 'I saw dead black birds' (on this page)
"It was hard to drive down the street in some places without running over them," said Robby King.
With the birds, a few stunned ones survived their fall and stumbled around like drunken revelers. There was little light across the countryside at the time, save for the glimmer of fireworks and some lightning on the horizon. In the tumult, many birds probably lost their bearings.
"I turn and look across my yard, and there's all these lumps," said Shane Roberts, who thought hail was falling until he saw a dazed blackbird beneath his truck. His 16-year-old daughter, Alex, spent Saturday morning picking them up. "Their legs are really squishy," the teen said.
For some people, the scene unfolding shortly before midnight evoked images of the apocalypse and cut short New Year's celebrations. Many families phoned police instead of popping champagne.
"I think the switchboard lit up pretty good," said Beebe police Capt. Eddie Cullum. "For all the doomsdayers, that was definitely the end of the world."
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Paul Duke filled three five-gallon buckets with dead birds on New Year's Day. "They were on the roof of the house, in the yard, on the sidewalks, in the street," said Duke.
The birds will not be missed. Large roosts like the one at Beebe can have thousands of birds that leave ankle- to knee-deep piles of droppings in places.
On Monday, a few live birds chirped and hopped from tree to tree behind the Roberts' home.
"The whole sky turns black every morning and every night," Roberts said.
At Duke's home, bird feeders stood empty. He fills them when bluebirds come in the summer but leaves them empty during blackbird season.
"They'd eat 50 pounds of feed a day," he said. "You couldn't keep them full."Video: Ark. birds died in mid-air, says official (on this page)
Bad weather was to blame for earlier bird kills in Arkansas.
In 2001, lightning killed dozens of mallards at Hot Springs, and a flock of dead pelicans was found in the woods about 10 years ago, Rowe said. Lab tests showed that they, too, had been hit by lightning.
In 1973, hail knocked birds from the sky at Stuttgart, Ark. Some of the birds were caught in a violent storm's updrafts and became encased in ice before falling from the sky. Some were described as bowling balls with feathers.Video: In Arkansas, it rained dead birds (on this page)
Rowe initially said poisoning was possible, but unlikely. Birds of prey and other animals, including dogs and cats, ate several of the dead birds and suffered no ill effects.
"Every dog and cat in the neighborhood that night was able to get a fresh snack," Rowe said.
David Lyons, the head of a local chapter of the Sierra Club, told msnbc.com that he was "waiting for the results of the pathology and toxicology tests before I make any judgments about the bird and fish kills.
"So far, the evidence does not suggest that pollution contributed to either the bird or fish kill," he added. "If the test results indicate that contaminants were responsible, then local environmental groups will likely have several questions and concerns about the two events."
NBC News, The Associated Press, Reuters and msnbc.com staff contributed to this report.