The Collaborative International Dictionary of English v.0.48:

Rhea \Rhe"a\, n. [L., a proper name.] (Zool.)
   Any one of three species of large South American ostrichlike
   birds of the genera Rhea and Pterocnemia. Called also the
   American ostrich.
   [1913 Webster]

   Note: The common rhea, or nandou (Rhea Americana), ranges
         from Brazil to Patagonia. Darwin's rhea (Pterocnemia
         Darwinii), of Patagonia, is smaller, and has the legs
         feathered below the knee.
         [1913 Webster]