cockatrice vs stem siren

cockatrice

noun
  • A legendary creature about the size and shape of a dragon or wyvern, but in appearance resembling a giant rooster, with some lizard-like characteristics. 

  • A snake or serpent that appears to be hatched of a rooster, or cock's, egg. 

  • The cobra. 

stem siren

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