I think angry birds changes the scene when all the birds have been "flung" and there is no movement left on the screen... But if you want to change it when many actors collide with the floor, you could set up a rule that counts a game attribute up each time an actor overlaps or collides with the floor, and then tell the game to change the scene when that number reaches a certain amount.
Or you could set up a boolean for each actor and tell the actors to change their boolean to true when they overlap or collide with the floor, and then tell the scene to change when all those booleans are true.
I'm sure there are a bunch of other ways, but that's what comes to mind initially...
Adding to what ekelrock said, you could great the booleans to check for a collision with all of them with the floor actor and then start a timer which then changes the scene after 3-5 seconds so that it isn't as abrupt. And then you could also interpolate the alpha on a transparent black box covering the screen to fade it to black and then change scene.
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Or you could set up a boolean for each actor and tell the actors to change their boolean to true when they overlap or collide with the floor, and then tell the scene to change when all those booleans are true.
I'm sure there are a bunch of other ways, but that's what comes to mind initially...
Good luck!
Endless ways to do it.