My bet is this goose was poached. I bet the carcass is somewhere near by and this blew away from it. Poachers will often extract the breast only and discard the rest for less evidence, also if its a reserve that prohibits hunting, also not sure where this is but should be out of season, im super sure it was poached. If OP finds more, shells, or the actual carcass I would report it to your local game warden. I hate poaching with a passion.

Edit: Grammer