Coldframe question

Last year I built a coldframe. My wife moved three flats of marigolds into it and something promptly ate the tops off of every one of them.... I didn't think anything ate marigolds! What do you suppose it was? Slugs? Cutworms? Mice?
Any suggestions to avoid the issue this year BEFORE I move plants out this year?
Thanks Ron H. in West Central Wisconsin
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Ron H wrote:

Chipmunks and some birds love Marigolds.
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Bill
In Hamptonburgh, NY
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