A little birdy told me if you fill these up partway with water and blow into them like a whistle, they warble like a songbird. This popular 18th century children's toy is painted ceramic, like many originals.
I tested on out when I got them and it whistles. They are very pretty. I got them for gifts.
Great find to add to our vintage bird whistle collection These bird whistles add so much color and interest, the children love them too. So reasonable bought a few