I tried the grass clod, the ping pong ball, had DH make them a little 'room' with 2 doors, and put in a branch. The grass clod is a hit - at first they craned their necks at it like an alien had landed, but now it's scattered everywhere and they are actually trying to take dust baths in the dirt! I haven't seen them do much with the ball, but it moves around so they must do something with it. They like their little room too - they all settled down there, so maybe they think it's a nest. And they've all hopped on the perch. Thanks for all the ideas - they're only 4 days old so the cabbage head is out there a ways.