partridge vs ruffed grouse

partridge

noun
  • Any bird of a number of genera in the family Phasianidae, notably in the genera Perdix and Alectoris. 

ruffed grouse

noun
  • An American game bird, Bonasa umbellus; the male makes drumming sounds with its wings 

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