This new sport already has a name: crowboarding.
(This page has a few more time-waste videos which may entertain.)
Strum the Sky said:
I'll never forget sleeping in a hut, backpacking the snowy mountains of New Zealand, and waking up early in the morning to hear a ruckus on the roof and cackling laughter and a carrying-on that got me up out of my warm sleeping bag in a good mood to check out what idiots outside were doing... Turned out it was a flock of kakapo (mountain parrots) on the roof... sliding on their backsides down the snowy corrugated tin roof from its peak, and then adroitly rolling over just at the edge of the lip and marching back up to the top to do it all over again, all of them cackling like kids and taking turns. Amazing. Watched it for half an hour.