Flextone Hunter Series Diver Duck Call The flextone design gives this call natural sound and the ability to change volume and tone. This easy to use call is deadly on Redheads, Cans, Bills, and Ring necks. Just squeeze the end for the deeper tones of Canvasbacks or Redheads. Leave the bell open for the higher pitch of Ring necks and Bluebills. You can also mix it up to sound like a whole raft of divers.