Pinhead vs yardbird

Pinhead

noun
  • A member of the Provisional IRA. 

yardbird

noun
  • A person who is imprisoned. 

  • A chicken. 

  • A soldier who is required to perform menial work on the grounds of a military base. 

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