bear hunter, it all depends on how your birds were wrapped when put in the freezer, and that the freezer is not a frost free freezer. Frost free freezer equals freezer burn immediately! If they were wrapped tightly in a good plastic bag, (not a wal-mart bag) and then double wrapped, you should be ok.
Freezer burn is very hard to combat in birds! The biggest problem you have is the head. If the head is badly freezer burned and not handled correctly, your mount will not turn out very good at all. The other problem area is the feet. The feet are easier to deal with if caught in time.
Given the species of birds you listed, I would not give up on them. Some of them are very hard to come by. Hope that helps. John