chirl vs skirl

chirl

noun
  • A kind of musical warble. 

verb
  • To emit a low sound; to warble. 

skirl

noun
  • A shrill sound, as of bagpipes. 

verb
  • To make a shrill sound, as of bagpipes. 

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