cowberry vs mountain bearberry

cowberry

noun
  • The berry of this shrub. 

  • A shrub native to the cool temperate areas of the Northern Hemisphere (Vaccinium vitis-idaea). 

mountain bearberry

noun
  • Arctostaphylos alpina; a species of bearberry. 

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