bush telegraph vs jungle telegraph

bush telegraph

noun
  • A system used by undeveloped societies in remote regions for communication over long distances, such as drum sounds, word-of-mouth relay, or smoke signals. 

  • A gossip network. 

jungle telegraph

noun
  • A system used by primitive cultures in remote tropical regions for communication over long distances, such as drum sounds or a relay of runners. 

  • A gossip network; an informal communication system within a group or organization. 

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