waul vs yowl

waul

verb
  • To wail, to cry plaintively. 

yowl

verb
  • Utter a yowl. 

  • Express by yowling; utter with a yowl. 

noun
  • A prolonged, loud cry, like the sound of an animal; a wail; a howl. 

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