Common Eiders are the largest ducks in North America. Adult males stand out in their black-and-white breeding plumage (also note their greenish nape), whereas brown-patterned females are easy to miss, especially when resting on seaweed-covered rocks. Immature males are mostly dark with a noticeably white chest.
Common Eiders spend much of their time close to shore, often frequenting coastal harbors, where they dive to feed on various shellfish, like Blue Mussels, and assorted crustaceans, like Green Crabs and Atlantic Rock Crabs. Back in 2014, I filmed a pair at the public beach in Biddeford Pool.