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):

Pterocnemia pennata
    n 1: smaller of two tall fast-running flightless birds similar
         to ostriches but three-toed; found from Peru to Strait of
         Magellan [syn: rhea, nandu, Pterocnemia pennata]