It's time to plan hunting trips. I know of two guide services that host Cape Cod duck hunting - mostly, but not only, sea ducks. November-January:
Cape Cod Sportsmen and East Coast Guide Service.
The latter even offers an Eider recipe: Eider Cape Cod. If you aren't planning to eat 'em, you shouldn't shoot 'em.
Here's one of Capt. Perez' Eider hunts in Cape Cod. These guys are good shots, and make it look far easier than it is even though Eiders decoy readily: