Gallinula chloropus vs moorhen

Gallinula chloropus

moorhen

noun
  • A female red grouse, Lagopus lagopus scotica. 

  • Any of various medium-sized water birds of the genus Gallinula, of the rail family, that feed in open water margins. 

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