night owl vs snowy owl

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. 

snowy owl

noun
  • A large, white, nomadic Arctic owl, Bubo scandiacus. 

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