A blues pianist and singer called Neal Roberts recorded a song called Wild Jack Blues in 1928 in Dallas, with animal imitations by Billiken Johnson. I starts:

"Wildjack's on the mountain and he brays the whole day long"

and ends

"I'm gonna keep my wildjack if I have to chain him down".

The rest of the song is in similar vein and it's obvious that Roberts is using a donkey to represent a phallic motif.

Anybody ever heard of a mountain donkey?