birdcage vs pigpen

birdcage

noun
  • A cage to keep pet or zoological specimen birds in. 

  • A game of chance played with dice; chuck-a-luck. 

pigpen

noun
  • A pigsty; an enclosure where pigs are kept. 

  • Something extremely dirty or messy. 

  • The pigpen cipher. 

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