The term 'Bay Duck' is a common name for the scaup, a species of diving duck found in coastal areas around the world. The scientific name for the scaup is Aythya marila, and it is also known as the greater scaup or just scaup. The scaup is a medium-sized duck, with males having a black head and neck, and females having a brown head and neck. The scaup is an important food source for many predators, including humans.