Arctic skua vs magnificent frigatebird

Arctic skua

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

magnificent frigatebird

noun
  • A species of frigatebird native to the tropical Atlantic, Fregata magnificens. 

How often have the words Arctic skua and magnificent frigatebird occurred in a corpus of books? (source: Google Ngram Viewer )