Update:
I had a small bag's worth of shredded paper, a mix of paper and cardboard. I put it in the nesting box.
They ate it.
Harrumph.
It doesn't seem to have caused any harm, though, thank goodness.
I had a small bag's worth of shredded paper, a mix of paper and cardboard. I put it in the nesting box.
They ate it.

It doesn't seem to have caused any harm, though, thank goodness.