horde vs rookery

horde

noun
  • A large number of people or things. 

  • A wandering troop or gang; especially, a clan or tribe of a nomadic people (originally Tatars) migrating from place to place for the sake of pasturage, plunder, etc.; a predatory multitude. 

verb
  • to travel en masse, to flock 

rookery

noun
  • A crowded tenement. 

  • A place where criminals congregate, often an area of a town or city. 

  • A colony of breeding birds or other animals. 

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