These "Dippy Birds" have been around for years, and you can't fool us - you've always wanted one. Now's your chance! But do you understand how it works? Do you get the complex relationship between chemistry and physics that makes this simple heat engine operate?
Is it a perpetual motion machine, or is it something more than that? Well, the answer is it's more than that. The Second Law of Thermodynamics states (paraphrased) that energy can neither be created nor destroyed in a closed system. So how does that relate to our little glass birdie here?
The goop in his butt is methylene chloride, which has a very low boiling point, and therefore evaporates quickly. At room temperature, one or two degrees temperature difference causes the bright red chemical to climb to his head. Suddenly topheavy, he falls over. The felt head, soaked in the water from the cup, cools the methylene chloride, and it drains back to the bottom. The bird rights itself, and it starts all over again.
Is this perpetual motion? Technically yes, but it's not energy for free! Temperature differentials drive the motor. That energy comes from the environment - from the sun. Is it efficient? Hardly, but it's still very cool.