The Collaborative International Dictionary of English v.0.48:

Buffel duck \Buf"fel duck\ (b[u^]f"f[e^]l d[u^]k`). [See
   Buffalo.] (Zool.)
   A small duck (Charitonetta albeola); the spirit duck, or
   butterball. The head of the male is covered with numerous
   elongated feathers, and thus appears large. Called also
   bufflehead.
   [1913 Webster]