For centuries, clay whistles had a primary function as a toy for children.
Nevetherless, a few folk traditions remind us that, before being a toy, the whistle had a more mysterious use, based on the fact the sound of the whistle originates from life-creating breath. Additionally, the shapes take us back to ancient European rituals.
But, as is usual with folk traditions, we must be carefull with any interpretation done in the name of a simplistic folklore. Every old feast where whistles were sold was not a survival of nature rebirth rites. Usually, these events just happened to be the yearly fair, a place of commerce, where potters sold their whistles to their customers'children.
Thus, all the rider-shaped whistles are not chthonic symbols every cuckoo is not a sign of spring.