The Collaborative International Dictionary of English v.0.48:

Ring-necked \Ring"-necked`\, a. (Zool.)
   Having a well defined ring of color around the neck.
   [1913 Webster]

   Ring-necked duck (Zool.), an American scaup duck (Aythya
      collaris). The head, neck, and breast of the adult male
      are black, and a narrow, but conspicuous, red ring
      encircles the neck. This ring is absent in the female.
      Called also ring-neck, ring-necked blackhead,
      ringbill, tufted duck, and black jack.
      [1913 Webster]