Smaller cavities are preferred because of less competition with the larger goldeneyes. It includes eiders, mergansers, goldeneyes and other sea ducks. There are many varieties of duck; buffleheads, goldeneyes, mallards, and cormorants. Common goldeneyes are diving birds that forage underwater. The bufflehead ("Bucephala albeola") is a small sea duck of the genus "Bucephala", the goldeneyes. The other "aberrant" merganser, the smew ("Mergellus albellus"), is phylogenetically closer to goldeneyes ("Bucephala"). Common goldeneyes are aggressive and territorial ducks, and have elaborate courtship displays. Barrow's goldeneyes tend not to share habitat with the much more numerous common goldeneye.