They've been a staple at Wrigley for a long time. Usually by now they're eating any leftover trash on the field and in the stands. I just never noticed them covering the field before until these last few games.
It looked like he was trying to re-enact the bat flip trick on Youtube that's been making the rounds recently. I was pumping gas this morning and it kept showing it on the tv's, I thought it was a cool little trick.