songbird vs songster

songbird

noun
  • A bird having a melodious song or call. 

  • Any bird in the passerine suborder Passeri, which are distinguished by a more sophisticated vocal apparatus 

songster

noun
  • A male songbird. 

  • A man who sings songs, especially as a profession; a male singer. 

  • One who writes songs. 

  • A book of songs; songbook. 

How often have the words songbird and songster occurred in a corpus of books? (source: Google Ngram Viewer )