When 47 birds fell from the sky in a Boston neighborhood on Thursday, it set off alarms.
It also set off some wild speculation. Was it poison? West Nile virus? High levels of methane gas in the atmosphere?
No one knows yet, as the cause remains under investigation. But it's not the first time something like this has happened. Maybe not in Boston, but in other parts of the country and across the globe, these sudden, mass bird deaths have been seen before.
In January of 2010, 5,000 blackbirds fell from the sky and died in one area in central Arkansas. In that case, the birds died from blunt-force trauma, apparently colliding with cars, trees, buildings and other stationary objects after being flushed out by fireworks. A year later, the same thing happened on a much smaller scale in the same town, with about 100 birds found dead.
"It just looked as if it had rained birds," a local city councilor said at the time.
Several days later, 500 dead birds - starlings, grackle and blackbirds - were found dead outside New Roads, Louisiana. Blunt-force trauma was determined to be a factor in their deaths as well, possibly from strong winds that forced the birds to fly through and collide with power lines.
That same day, between 50 and 100 jackdaws were found dead on a street in Sweden. They also are believed to have died as a result of blunt-force trauma related to fireworks.
A day later, several hundred dead birds were found dead in western Kentucky. Tests ruled out diseases or poisons.
One day after that, hundreds of turtle doves were found dead in Faenza, Italy. Their deaths were attributed to overeating and indigestion.
And less than a week later, over a hundred dead birds were found along a highway in California. Officials said the birds were hit by a truck, calling it "a massive case of roadkill."
No link has ever been discovered between any of these cases.
In Boston, investigators are still trying to figure out what caused the birds to fall ill.
Fifteen of the 47 birds that were found survived. The remaining birds have been sent to Tufts University for testing.
"We don't know what is going on," said John Meany from Boston Inspectional Services.