gallinule vs sultana bird

gallinule

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

sultana bird

noun
  • A purple swamphen, Porphyrio porphyrio. 

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