lesser kestrel vs merlin

lesser kestrel

noun
  • A small falcon, Falco naumanni. 

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 lesser kestrel and merlin occurred in a corpus of books? (source: Google Ngram Viewer )