I don’t know what this is. From everything I’ve found, this is real. There have been some explanations but they all seem about as convincing as, “It was a weather balloon.”
I don’t really have much more to say. I’ve added a bunch of links to various news sources…
https://www.cnn.com/2022/02/18/world/blackbird-swarm-crash-mexico-scn/index.html
https://cbs12.com/news/local/video-shows-hundreds-of-birds-falling-out-of-the-sky-in-mexico
https://www.theguardian.com/environment/2022/feb/14/why-did-birds-fall-from-sky-in-mexico-probably-a-predator-experts-say-aoe
https://www.ksat.com/news/2022/02/16/viral-video-shows-hundreds-of-birds-fall-from-sky-in-mexico/