black-crowned night heron vs heron

black-crowned night heron

noun
  • A medium-sized heron, Nycticorax nycticorax, found throughout a large part of the world, except in the coldest regions and Australasia. 

heron

noun
  • A long-legged, long-necked wading bird of the family Ardeidae. 

How often have the words black-crowned night heron and heron occurred in a corpus of books? (source: Google Ngram Viewer )