The Collaborative International Dictionary of English v.0.48:

Snowbird \Snow"bird\, n. (Zool.)
   (a) An arctic finch (Plectrophenax nivalis syn.
       Plectrophanes nivalis) common, in winter, both in
       Europe and the United States, and often appearing in
       large flocks during snowstorms. It is partially white,
       but variously marked with chestnut and brown. Called also
       snow bunting, snowflake, snowfleck, and
       snowflight.
   (b) Any finch of the genus Junco which appears in flocks in
       winter time, especially Junco hyemalis in the Eastern
       United States; -- called also blue snowbird. See
       Junco.
   (c) The fieldfare. [Prov. Eng.]
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Snowflake \Snow"flake`\, n.
   1. A flake, or small filmy mass, of snow.
      [1913 Webster]

   2. (Zool.) See Snowbird, 1.
      [1913 Webster]

   3. (Bot.) A name given to several bulbous plants of the genus
      Leucoium (Leucoium vernum, Leucoium aestivum, etc.)
      resembling the snowdrop, but having all the perianth
      leaves of equal size.
      [1913 Webster]

WordNet (r) 3.0 (2006):

snowflake
    n 1: a crystal of snow [syn: snowflake, flake]
    2: white Arctic bunting [syn: snow bunting, snowbird,
       snowflake, Plectrophenax nivalis]