I heard on a podcast (The Animal Turn, season 4) that starlings move in an algorithm of 7. So whenever that number is disrupted, they move. I’m not sure I’m doing that fact any justice, but it was really interesting. Probably the 3 or 4 episode (at the very end) if you’re interested in the podcast.
Not only a brilliant musician, but also Jack Black’s (late father-in-law).