chirr vs chitter

chirr

verb
  • To make the prolonged trilling sound of an insect (e.g. a grasshopper, a cicada). 

noun
  • The trilled sound made by an insect. 

chitter

verb
  • To make a series of high-pitched sounds; to twitter, chirp or chatter. 

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