Basically unmistakable and is just what the name says: a swan with a black neck. It also sports a bright red knob where the beak meets the head, a feature that is enlarged on males during breeding season.
A couple of Black-necked Swans at Swan Lake Iris Gardens, Sumter, SC.
Will be posting images from a recent camera club field trip to Swan Lake Iris Gardens, Sumter, South Carolina. It is currently the only public park in the United States to have all eight species of swans—including Royal White Mutes, Black Necks, Coscorobas, Whoopers, Black Australians, Whistlers, Bewicks, and Trumpeters.