The dunking bird, also known as the drinking bird, is a fascinating toy that demonstrates principles of thermodynamics and fluid mechanics. It’s essentially a heat engine that converts thermal energy into mechanical motion. The toy is mistakenly considered to exhibit perpetual motion because the toy appears to move on its own. But there is a temperature difference between the bird’s head and the glass bulbs containing water. The dunking bird uses the continuous evaporation from the bird’s head to drive its motion.