kestrel vs peregrine hawk

kestrel

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

  • The common kestrel, Falco tinnunculus. 

peregrine hawk

noun
  • The peregrine falcon. 

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