What feature primarily distinguishes a male King Eider from a male Common Eider on the head and bill?

Answer

A large, distinctive orange or reddish knob at the base of the bill.

The male King Eider is primarily identified by the large, noticeable orange or reddish knob structure situated at the base of its bill, which is absent on the Common Eider male.

What feature primarily distinguishes a male King Eider from a male Common Eider on the head and bill?
birdidentificationduckEider