bittern vs grey heron

bittern

noun
  • Several bird species in the Botaurinae subfamily of the heron family Ardeidae. 

  • The saline substance added to soy milk to coagulate it as a primary step in the production of tofu. 

  • The liquor remaining after halite (common salt) has been harvested from saline water (brine). 

grey heron

noun
  • Ardea cinerea, an Old World wading bird of the heron family. 

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