chirl vs vocalize

chirl

verb
  • To emit a low sound; to warble. 

noun
  • A kind of musical warble. 

vocalize

verb
  • To produce noises or calls from the throat. 

  • To sing without using words. 

  • To add vowel points to a consonantal script (e.g. niqqud in Hebrew) 

  • To express with the voice, to utter. 

  • To turn a consonant into a vowel. 

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