cowberry vs foxberry

cowberry

noun
  • The berry of this shrub. 

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

foxberry

noun
  • The berry of this plant. 

  • The plant cowberry or lingonberry, Vaccinium vitis-idaea. 

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