In a scene straight out of an Alfred Hitchcock film, hundreds of birds have been found dead outside the NASCAR Hall of Fame.
It's believed an entire flock flew into the side of the building in Charlotte, North Carolina.
Nonprofit Carolina Waterfowl Rescue received a call at 11pm on Tuesday night (local time) from a witness who said dozens of birds were diving straight at the building's windows.
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Rescuers arrived on the scene to find more than 300 chimney swifts, a third of which were already dead, The Charlotte Observer reports.
Video taken by a woman who works in the Hall of Fame building shows the footpath scattered with the motionless bodies of birds. What looks to be an injured bird can be seen dropping to the ground after hitting the window.
"Don't let them hit you, there's obviously something wrong with them," the woman filming can be heard saying. "But it's a whole flock. That's odd."
A security guard can be heard saying the birds had been flinging themselves into the building for an hour.
"This is like something out of a f**king move," the woman says.
She posted the footage to Facebook, and later wrote that after some time many of the unconscious birds woke up and began flinging themselves against the building again.
Carolina Waterfowl Rescue is now asking for donations to help them treat about 100 "severely injured" birds.
"The other third appears stunned and will hopefully be released in a few days," the organisation says.
Approximately one billion birds die in the US every year from flying into windows, usually in autumn during migration season.