That is exactly what you say. "Looking for gifted birds for taxidermy. Of course, I will pay for shipping." You can word it as friendly as you want, but you can not be charged, nor pay for any handling or packaging fees, just the cost of shipping. You'd be surprised at how many people have ducks that may be uncommon for you that are as common for them, that would be willing to gift a bird or two for a taxidermy collection.
Here is the link to the Federal game laws regarding the particulars:
http://ecfr.gpoaccess.gov/cgi/t/text/te ... ain_02.tpl
I tried the link myself, but my Adobe Reader was malfunctioning, so good luck. I know it works, because I've referred to it many times in the past.
Can you be more specific on what you are questioning? Are you asking how to ship a bird so it remains in good condition for taxidermy purposes, or are you asking how to ship it to make it legal? I've got an answer for both, you have to insulate the box pretty good, and ship it two-day maximum, and preferably in the winter months, and it has to be tagged with the hunters name, species of duck, where it was harvested, when it was harvested, the license number or the hunter who harvested the bird, and a signature, all tagged to the foot of the duck. If you want more specifics, please ask your question. Please look at the link I provided for Champ, and you'll find what you're looking for on the legalities if you are indeed inquiring about that.