Fluid inside condenses from the evaporative cooling of the water off the bird’s beak, making it top heavy and dunking it back into the water
The condensate rejoins the liquid pool in the bird’s bulb, and he tips up again
Process continues indefinitely
The fluid and dye inside the bird can permanently stain, and the bird’s glass body can easily be broken
Children are fascinated by the bobbing bird, and the educational possibilities are great.