little owl vs night owl

little owl

noun
  • A species of small European owl, Athene noctua. 

night owl

noun
  • An owl (order Strigiformes) that is nocturnal. 

  • A musical instrument which imitates an owl's hoot, consisting of a receptacle partly filled with water and a mouthpiece that is blown into. 

  • One who goes to bed late, or stays up late at night or in the early hours of the morning. 

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