lone wolf vs rara avis

lone wolf

noun
  • A person who avoids the company of others; a loner; an independent or solitary person. 

  • A wolf that is not part of a pack. 

  • A criminal who acts alone, not as part of a group. 

rara avis

noun
  • A rare or unique, and thus outstanding or unusual, person or thing; a rare bird. 

  • A rare species or type of bird. 

How often have the words lone wolf and rara avis occurred in a corpus of books? (source: Google Ngram Viewer )