The Collaborative International Dictionary of English v.0.48:

meadowlark \meadowlark\, meadow lark \meadow lark\n. (Zool.),
   Any species of Sturnella, a genus of North American
   songbirds allied to the starlings. The common species
   (Sturnella magna) has a yellow breast with a black
   crescent.

   Syn: lark.
        [1913 Webster + WordNet 1.5] Meadowsweet

WordNet (r) 3.0 (2006):

meadowlark
    n 1: North American songbirds having a yellow breast [syn:
         meadowlark, lark]