cattle call vs convocation

cattle call

noun
  • An audition which is open to the public and thus draws a large number of applicants, many of whom are inexperienced. 

convocation

noun
  • An assembly or meeting. 

  • The act of calling or assembling by summons. 

  • An assembly of the clergy, by their representatives, to consult on ecclesiastical affairs. 

  • An academic assembly, in which the business of a university is transacted. 

  • A flock of eagles. 

How often have the words cattle call and convocation occurred in a corpus of books? (source: Google Ngram Viewer )