A security camera in Mexico captured wild and unnerving footage last week that has since gone viral. In a startling wave of plummeting birds, a huge flock of yellow-throated blackbirds was captured crashing to the ground in Ciudad Cuauhtemoc, in western Chihuahua, in the latest case of mass bird die-off. While many recover quickly, others don’t appear so lucky. The video has had people wondering if it's real.

You can watch the incident below, though be warned, it contains content some may find distressing. 

The footage was captured on a security camera on February 7 and was reported by local media outlets before being confirmed as real by fact-checking website Snopes. Further footage was then posted walking through the field of dead birds, described as "hundreds" by local media outlet El Heraldo de Chihuahua. It's thought they were migrating south from Canada.  

While it is understandable some may believe the footage fake, cases of large flocks of birds suddenly falling from the sky are not particularly rare, albeit extremely bizarre to witness. 

Why exactly does it happen? The jury is still out, but the most likely theory is the tightly-packed flock was reacting to a predator. Smaller birds like blackbirds are preyed on by larger birds of prey, and the sight of such a predator will send the flock into a frenzy. The entire group darts towards the ground, and the unlucky few on the bottom will slam into the ground, often killing them instantly. 

“This looks like a raptor-like a peregrine or hawk has been chasing a flock, like they do with murmurating starlings, and they have crashed as the flock was forced low,” ecologist Dr Richard Broughton told the Guardian.  

“You can see that they act like a wave at the beginning, as if they are being flushed from above.”