kestrel vs merlin

kestrel

noun
  • Any of various small falcons of the genus Falco that hover while hunting. 

  • The common kestrel, Falco tinnunculus. 

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. 

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