barn swallow vs martin

barn swallow

noun
  • Hirundo rustica, the most widespread species of swallow in the world; a distinctive passerine bird with blue upperparts, a long, deeply forked tail and curved, pointed wings, is found in Europe, Asia, Africa and the Americas. 

martin

noun
  • Any of various passerine birds of the family Hirundinidae, which also includes swallows, that catch insects whilst flying. 

  • A perforated stone-faced runner for grinding. 

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