Arctic skua vs Portuguese man-of-war

Arctic skua

noun
  • A seabird (Stercorarius parasiticus), of the skua family (Stercorariidae) 

Portuguese man-of-war

noun
  • Physalia physalis, a marine cnidarian consisting of a floating colony of hydrozoans attached to a float, superficially resembling a jellyfish. 

  • Used other than figuratively or idiomatically: see Portuguese, man-of-war. 

How often have the words Arctic skua and Portuguese man-of-war occurred in a corpus of books? (source: Google Ngram Viewer )