I first heard of these reading Joel Chandler Harris' Uncle Remus stories. He called them "Wull-er-de-Wust" [1].
[1] https://www.gutenberg.org/files/24430/24430-h/24430-h.htm#V
replies(3):
[1] https://www.gutenberg.org/files/24430/24430-h/24430-h.htm#V