I took a broad leaf fern (don't know genus, sorry) from my friend's back yard and potted it in a spagnum / peat mix. I made sure to take all the roots and a bit of the substrate around it. The fern seemed very happy till the cats ate its poor leaves off. I dug a few cm into the substrate and saw several fiddleheads forming, so I kept the dear around. One of the fiddleheads was about to unfurl yesterday. I came in this morning and the very small tip of the fiddlehead seems a darkish green. What would have become of the leaves are now brownish. How did this change happen so dramatically? What can I do to prevent this from happening to the three other fiddleheads that'll be starting to unfurl in the next several days?

I should say that the fern is now at work, and thus safe from the cats. The indirect light from the office comes from a Southern facing window. Perhaps that is too much light?

The plant is in a clay pot and gets plenty of water. I even mist the fiddleheads several times a day. I've put some moss on top of the soil to help preserve moisture as well.