I saw that video. Very interesting, even fascinating.
My first thought was; When do they know it’s time to stop?
I am guessing the ones on the outside of the circle will know when any predator has left the area, so the outside fringes will begin to slow and disperse. Sort of like a slowly unraveling ball of yarn, peeling away to the center.
Probably takes quite a while. There is no loud Buzzer, as with a Basketball Game.
Last in run has a whistle