The bufflehead (_Bucephala albeola_) and the goldeneye (_Bucephala clangula_) are two species of diving ducks that are closely related and physically similar. Both species have a dark brown head and back, with white underparts and a white patch on the side of the head. However, there are some key differences between the two species that can help you to identify them in the field.
One of the most obvious differences between the bufflehead and the goldeneye is their size. The bufflehead is a smaller duck, with a body length of around 14-16 inches and a wingspan of around 22-24 inches. The goldeneye, on the other hand, is a larger duck, with a body length of around 17-19 inches and a wingspan of around 26-28 inches.