The Collaborative International Dictionary of English v.0.48:

mockingbird \mockingbird\, mocking bird \mocking bird\n.
   (Zool.),
   A long-tailed gray-and-white songbird of North America
   (Mimus polyglottos), remarkable for its exact imitations of
   the notes of other birds. Its back is gray; the tail and
   wings are blackish, with a white patch on each wing; the
   outer tail feathers are partly white. Originally its range
   was confined mostly to the southern states, but by late 19th
   century it had migrated as far north as New York. The name is
   also applied to other members of thee same and related
   genera, found in Mexico, Central America, and the West
   Indies, such as the blue mockingbird of Mexico, Melanotis
   caerulescens.

   Syn: mocker, Mimus polyglottos .
        [WordNet 1.5]