heron vs night heron

heron

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

night heron

noun
  • Any of the nocturnal species of herons of the genera Nycticorax, Nyctanassa, and Gorsachius. 

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