gallinule vs moorhen

gallinule

noun
  • A bird of one of several species in the genera Porphyrio and Gallinula of the family Rallidae. 

moorhen

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

  • A female red grouse, Lagopus lagopus scotica. 

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