dunnock vs selfheal

dunnock

noun
  • A small European and Asian passerine bird, Prunella modularis; the hedge sparrow or hedge warbler. 

selfheal

noun
  • A small, herbaceous European plant with blue-violet flowers from any species of genus Prunella. 

  • Especially, Prunella vulgaris. 

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