songster vs vocalist

songster

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

  • One who writes songs. 

  • A male songbird. 

  • A book of songs; songbook. 

vocalist

noun
  • A singer; a person who likes to sing. 

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