oooh i kept meaning to post a topic on here about that! ours go bonkers when they see me with the rake and love rummaging through them, eating the little greenflies, bugs etc.
my run isn't covered and i just put the leaves in a pile in the corner; figured they will rot down eventually (might remove them for the compost heap though - like that idea..) i have some big pieces of drift wood there too, complete with large wormholes (woodlice/slugs go into the holes on the underside and every so often i turn the logs over and give the hens a treat)
another thing i do is to put soil from the pots that i grew my sweet peas etc in -- it's full of worms, little slugs etc and the hens really enjoy scratching through it to get to the goodies.
