crooner vs songbird

crooner

noun
  • One who croons; a singer, usually male, especially of popular music. 

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 

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