The Greater and Lesser Scaup can be hard to tell apart. On the Greater Scaup the high point of the head is ahead or over the eye whereas on the Lesser Scaup the high point of the head is behind the eye. The Lesser Scaup also has a flat topped head while the Greater Scaup's head is rounded like it was drawn with a compass. These differences are most evident in breeding males. These birds are called Blue Bills in some areas.
Even when one knows all this separating the species can still be tricky. Bring your bird identification book.
................and please feel free to correct my identification but please tell me where I went wrong:)
