kestrel vs sparrowhawk

kestrel

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

  • The common kestrel, Falco tinnunculus. 

sparrowhawk

noun
  • Any of numerous other relatively small Old World species of Accipiter, that prey on smaller birds or otherwise resemble A. nisus. 

  • The Eurasian sparrowhawk, Accipiter nisus, a small, short-winged European hawk that preys on smaller birds. 

  • A female such bird, a male being a musket. 

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