human chain vs migration

human chain

noun
  • A form of demonstration in which people link their arms as a show of political solidarity. 

  • A bucket brigade. 

migration

noun
  • Movement in general. 

  • Instance of changing a platform from an environment to another one. 

  • The movement of cells in particular directions to specific locations. 

  • Seasonal moving of animals, as mammals, birds or fish, especially between breeding and non-breeding areas. 

  • An instance of moving to live in another place for a while. 

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