North American bison vs North American buffalo

North American bison

noun

  • Bison bison (“B. bison”); Synonym of American bison (“American buffalo”) 

North American buffalo

noun

  • Bison bison (“B. bison”); Synonym of American bison (“American buffalo”) 

How often have the words North American bison and North American buffalo occurred in a corpus of books? (source: Google Ngram Viewer )