churr vs ululate

churr

verb
  • To make the low vocal sound of some birds. 

noun
  • A low vocal sound made by some birds. 

ululate

verb
  • to produce a rapid and prolonged series of sharp noises with one's voice. 

  • to howl loudly or prolongedly in lamentation or joy 

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