I highly doubt that your problem is caused by a bird. This year my friend's perfect little seedling got nibbled on by some sort of bug. The day it popped out of the soil both of the cotyledon were lush and green. Next day, there was a good portion missing from the leaves. She is a trouper though; after four days it's still standing with the same two (partial) leaves. A deer stepped 2 inches away from the seedling too.
Anyways, if the seedling has less than 3 pairs of leaves, u should be fine. Infestations on such small plants usually aren't perminent. If it's spider mites u should be worried though.