The Collaborative International Dictionary of English v.0.48:

Mocking \Mock"ing\, a.
   Imitating, esp. in derision, or so as to cause derision;
   mimicking; derisive.
   [1913 Webster]

   Mocking thrush (Zool.), any species of the genus
      Harporhynchus, as the brown thrush (Harporhynchus
      rufus).

   Mocking wren (Zool.), any American wren of the genus
      Thryothorus, esp. Thryothorus Ludovicianus.
      [1913 Webster] mockingbird

WordNet (r) 3.0 (2006):

mocking thrush
    n 1: thrush-like American songbird able to mimic other birdsongs
         [syn: thrasher, mocking thrush]