Hundreds of yellow-headed blackbirds fell from the sky, and about 100
appeared to die, in Chihuahua, Mexico, on Feb. 7.

The flock of blackbirds quickly descended upon a Chihuahua neighborhood
street in footage shared by Reuters, briefly blackening the sky. Most of
the birds continued flying in different directions, but dozens remained
on the ground, seemingly dead.

Several theories have spread about the cause of the birds’ sudden
descent or death. A veterinarian suggested that inhalation of toxic
fumes, possibly from a heater, caused the bizarre incident, according to
the Chihuahua Herald. The newspaper also speculated that the birds may
have been electrocuted while sitting on a power line.

Richard Broughton, an ecologist at the UK Centre for Ecology &
Hydrology, told the Guardian that a predatory bird, such as a raptor,
was the likely cause. Raptors chase flocks of birds, causing them to fly
tightly together before crashing into the ground, he explained.

The Independent suggested that blame for the bird deaths may lie with
high levels of air pollutants. There have been several incidents of
large numbers of migratory birds dropping dead in New Mexico, according
to the Independent. The birds that crashed in Chihuahua were migratory
birds from Canada, the outlet said.

https://www.wnd.com/2022/02/watch-hundreds-blackbirds-mysteriously-drop-dead-mid-flight/