black-headed gull vs loon

black-headed gull

noun
  • A small gull, Chroicocephalus ridibundus, which breeds in much of Europe and Asia, and also in coastal eastern Canada. 

loon

noun
  • Any of various birds, of the order Gaviiformes, of North America and Europe that dive for fish and have a short tail, webbed feet and a yodeling cry. 

  • A crazy or deranged person; a lunatic. 

  • A boy, a lad. 

  • An English soldier of an expeditionary army in Ireland. 

  • A simpleton. 

  • A harlot; mistress. 

How often have the words black-headed gull and loon occurred in a corpus of books? (source: Google Ngram Viewer )