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]

The Collaborative International Dictionary of English v.0.48:

Nandou \Nan"dou\, Nandu \Nan"du\, n. [Braz. nhandu or yandu.]
   (Zool.)
   Any one of three species of South American ostriches of the
   genera Rhea and Pterocnemia, especially the smallest,
   Pterocnemia pennata (formerly Rhea Americana), called
   also the common rhea. They are tall fast-running flightless
   birds similar to ostriches but three-toed, found from Peru to
   the Straits of Magellan. See Rhea. [Written also nandow.]
   [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

Rhea americana
    n 1: larger of two tall fast-running flightless birds similar to
         ostriches but three-toed; found from Brazil to Patagonia
         [syn: rhea, Rhea americana]