Why canaries are yellow (WTF - Weird Things in Folktales)

Welcome to my A to Z Challenge blog series titled WTF - Weird Things in Folktales! Find the introduction post (explaining the theme) here. Find all other participating blogs in the comments of each day's post on the main blog! You can also follow us on Twitter and Facebook.
Y is the third and final letter that has been excluded from the Motif Index. Once more, I searched for words that start with