ptarmigan vs red grouse

ptarmigan

noun
  • Any of three species of small grouse in the genus Lagopus found in subarctic tundra areas of North America and Eurasia. 

red grouse

noun
  • A medium-sized bird, Lagopus lagopus scotica, of the grouse family, found in heather moorland in Great Britain and Ireland. 

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