The Collaborative International Dictionary of English v.0.48:

Songster \Song"ster\ (s[o^]ng"st[~e]r), n. [AS. sangestre a
   female singer.]
   1. One who sings; one skilled in singing; -- not often
      applied to human beings.
      [1913 Webster]

   2. (Zool.) A singing bird.
      [1913 Webster]

WordNet (r) 3.0 (2006):

songster
    n 1: a composer of words or music for popular songs [syn:
         songwriter, songster, ballad maker]
    2: a person who sings
    3: any bird having a musical call [syn: songbird, songster]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "songster":
   Heldentenor, Meistersinger, Philomel, alto, aria singer,
   arrangement, baritenor, baritone, bass, basso, basso buffo,
   basso cantante, basso profundo, blues singer, bulbul, canary,
   cantatrice, cantor, caroler, chanter, chantress,
   coloratura soprano, comic bass, contralto, copy, countertenor,
   crooner, cuckoo, deep bass, diva, draft, dramatic soprano, edition,
   feathered songster, heroic tenor, hymnal, hymnbook, hymner,
   improvisator, instrumental score, lark, lead singer, libretto,
   lieder singer, lute tablature, mavis, melodist, mezzo-soprano,
   mockingbird, music, music paper, music roll, musical notation,
   musical score, nightingale, notation, opera, opera score,
   opera singer, orchestral score, oriole, part, piano score,
   prima donna, psalm singer, ringdove, rock-and-roll singer, score,
   sheet music, short score, singer, singing bird, singstress,
   song sparrow, songbird, songbook, songstress, soprano, tablature,
   tenor, text, thrush, torch singer, transcript, transcription,
   version, vocal score, vocalist, vocalizer, voice, warbler,
   written music, yodeler