merlin vs windhover

merlin

noun
  • A small falcon, Falco columbarius, that breeds in northern North America, Europe, and Asia. 

  • A cytoskeletal protein active in the suppression of tumors. 

windhover

noun
  • The common kestrel (Falco tinnunculus). 

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