Hi, 

While most ferns are considered tolerant of deer and rabbit browsing, that doesn't necessarily mean that they won't be sampled. That is probably what is going on here, especially since it was left on the ground like this. 

You can cage it with some simple chicken wire or a wire mesh trash can if it fits, or some netting so it can get better established before some sampling may occur. 

Are the stems soft and mushy at all, as if they could be rotting from being too wet? Maiden ferns do like a moist and humid environment but the soil should be fertile and well draining still. 

Feel free to send a photo of the entire plant if you think that could be helpful as well. 

Emily