The infamous drinking bird has been popular amongst adults and children for many decades. The Drinking Bird works using properties of thermodynamics, converting thermal energy into mechanical energy. How does it work? First dunk your birds head in his drinking glass. The birds wet head cools from evaporation - that condenses with the liquid vapours in the head creating a partial vacuum. The liquid in the body is warmer hence at higher pressure and rises up the tube to fill the lower pressure head. When it tilts forward it lets the liquid drain back and the cycle repeats. The process continues indefinitely. No batteries required.