barn swallow vs house 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. 

house martin

noun
  • A migratory passerine bird of the swallow family, genus Delichon 

  • The common house martin (Delichon urbicum). 

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