The Collaborative International Dictionary of English v.0.48:

Guacharo \Gua*cha"ro\, n. [Cf. Sp. gu['a]charo sickly,
   dropsical, guacharaca a sort of bird.] (Zool.)
   A nocturnal bird of South America and Trinidad (Steatornis
   Caripensis, or S. steatornis); -- called also oilbird.
   [1913 Webster]

   Note: It resembles the goatsuckers and nighthawks, but feeds
         on fruits, and nests in caverns. A pure oil, used in
         place of butter, is extracted from the young by the
         natives.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Steatornis caripensis
    n 1: nocturnal fruit-eating bird of South America that has fatty
         young yielding an oil that is used instead of butter [syn:
         oilbird, guacharo, Steatornis caripensis]