Source : Webster's Revised Unabridged Dictionary (1913)

Whooper \Whoop"er\, n.
   One who, or that which, whooops.

   {Woopher swan}. (Zo["o]l.) See the Note under {Swan}.

Source : WordNet®

whooper
     n 1: rare North American crane having black-and-white plumage and
          a trumpeting call [syn: {whooping crane}, {Grus
          americana}]
     2: common Old World swan noted for its whooping call [syn: {whooper
        swan}, {Cygnus cygnus}]