Lots of theories as to why birds like this flock of Starlings can perform an aereobatic show without crashing into each other. Some believe the birds are simply ultra-coordinated in one or more flight parameters: turning, spacing, velocity, flight direction, etc.
Others take the scientific approach: "When air passes over a mass, it creates a wake. (Newton's theorem). Birds somehow have this in them to sense the eddy currents behind the bird ahead of it. It tries to keep in balance (I don't know how) and it stays in perfect sync and rhythm in float on a cushion of air."
One English ornithologist said, and I quote, "If we are talking of birds of the same feathers flying together as in groups ..the answer is that like you and I...BIRDS HAVE EYES TO SEE where they are going..since their means of movement is thru flight..their INSTINCT tells them how far they are from each other guiding their velocity and manuevering to avoid collision or hitting each other inflight. I WOULDN'T BE SURPRISED IF THEY DIDN'T HIT EACH OTHER BECAUSE THEY HAVE EYES TO SEE...BUT RATHER I WOULD BE SURPRISED TO SEE BLIND BIRDS FLYING WITHOUT HITTING EACH OTHER!!!"
I'm still confused. Anyhow...Enjoy the video!