kestrel vs windhover

kestrel

noun

  • The common kestrel, Falco tinnunculus. 

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

windhover

noun

  • The common kestrel (Falco tinnunculus). 

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