Dark-eyed Junco feeding on moss

A few times every winter I notice Dark-eyed Juncos picking something from the moss clumps on my Vine Maple tree, and eating whatever they are finding. I'm still trying to determine for certain which part they are eating. I suspect it is the spore cases, or "sporangia." You can see some of the action in this video clip by copying and pasting it into your browser's address line:

http://www.youtube.com/watch?v=Rtb3D6H7_8A