There appears to be a relationship with the concept of the Boto (the fresh-water porpoise found in the Amazonas River and its tributaries) having shape-shifting abilities and then while in the form of a human male having sexual relations with young women.
The Boto, or Amazon River Dolphin, is also known to inhabit the Orinoco River system.
In the region of Aragon, especially in the town of Huesca, the dulzaina is played along with gaitas de boto, regional bagpipes, and sometimes drums.