What is really is amazing is that scientist have recorded them, frame by frame, and timed how long the group makes a turn, timing from the first bird changing direction until the last one.
Then they take individual birds, in a cage or something, and time their individual reaction time.
Turns out the group makes a turn faster then the individual time of each birt.
…nobody can explain it.
David Attenborough phrases it; "as if they fly with one mind"