Be sure to have a bag with date, species , your name, address on the bag that it goes in to... I have read up on this subject in regards to what counts as possesion and it falls under the daily bag and possession limits set by the feds. ( species specific for mergansers) It also refers to the edible portions of the bird as being the part that counts. The easy fix is to clip the wings of the bird and use them on a bumper and it should not count towards your possesion limit. So if you have this in possession while training in it does fall in the daily bag limit for mergansers.
As I tie flies and keep the feathers of the ducks that I shoot, they are not considered part of the possesion limit as you cant really eat them and people that tie flies would be getting knocks on the door from the FEDS..
FYI it also falls under the possession limit for ducks, it is counted in the total number of birds that you possess...home, car, truck, fridge... I have read about people down south getting busted for having more ducks than legally allowed, I have yet to hear of a person up in MA to have recieved a ticket for total possesion of birds at home.
There is one loophole to the federal possesion limits, you ARE able to hunt ducks up to your daily bag/possesion limit, then gift them to another member of your houshold each member (who may or may not hunt) but are able to possess game shot and killed by another hunter up to their possesion limit. It seems like a whole lot of work but basically your name on freezer bag and address and person you gifted them to in your household.
The possesion and bag limits are set to prevent "market hunting" and really should not be abused. I am not advocating taking more than you will use just because you can or exceeding your daily bag limit as it is still illegal to shoot more than your 6 ducks in one day. But it can keep you hunting longer into the season. Or eat what you shoot while the season is going on.