CHIHUAHUA, Mexico (NewsNation Now) — A viral video of dozens of birds falling from the sky in Mexico baffled the internet and sent many searching for theories. But an avian expert says it’s more common than you may think.

The security video out of Chihuahua, Mexico, showed a large number of birds suddenly drop dead mid-flight and rain down on a home and the adjacent street.

Sectional police of Alvaro Obregon reported that the incident involved close to 100 yellow-headed blackbirds that were migrating from northern Canada to Mexico for the winter.

A local veterinarian reported to police the birds could have died after inhaling toxic fumes from a heater nearby or due to an overcharge from electricity cables.

Dr. Nat Seavy, director of migration science for the National Audubon Society, told NewsNation events such as these have happened before.

“Back in 2010-2011, there was a case with blackbirds where a large number of them in the middle of the night were frightened — they were disturbed by fireworks — and many of them collided with buildings, and there was a number of mortality there,” Seavy said.

As to what caused the incident in Mexico, Seavy said it could have been a number of things and blackbirds may be at unique risk.

“One of the things that’s unique about this particular species and a number of other related species … is that they form these incredibly dense flocks,” he said. “A lot of people might be familiar with some of the videos of these incredibly dense flocks that wheel around in the air; they’re called murmurations. And they’re absolutely spectacular. It seems that this was a case where one of those blocks rather than being inspiring, something went awry.”

Seavy believes the answer to what caused the birds to fall from the sky may never be known.

“To me, this looks like it was likely something that could have caused some sort of other disturbance, whether it was a predator or something else going on in the environment that caused these birds to collide into the ground,” he said.