The Collaborative International Dictionary of English v.0.48:

Kinglet \King"let\, n.
   1. A little king; a weak or insignificant king. --Carlyle.
      [1913 Webster]

   2. (Zool.) Any one of several species of small singing birds
      of the genus Regulus and family Sylviid[ae].
      [1913 Webster]

   Note: The golden-crowned kinglet (Regulus satrapa), and the
         rubycrowned kinglet (Regulus calendula), are the most
         common American species. The common English kinglet
         (Regulus cristatus) is also called golden-crested
         wren, moonie, and marigold finch. The kinglets are
         often popularly called wrens, both in America and
         England.

WordNet (r) 3.0 (2006):

Regulus calendula
    n 1: American kinglet with a notable song and in the male a red
         crown patch [syn: ruby-crowned kinglet, ruby-crowned
         wren, Regulus calendula]