At first sight our Bird, also called Drinking Bird or Dippy Bird, appears to be just a toy. But in fact it demonstrates a lot of thermodynamic phenomena: cooling by evaporation, the dependence of vapor pressure on temperature and the resulting force on a liquid column from the vapor pressure. The wet bird's head is cooled by the evaporation of the water, reducing the pressure above the blue fluid inside the bird's neck. As the pressure above the liquid column is lower than that below it, the column of liquid is forced upwards, changing the center of mass and making the whole bird swing around the axis between his legs ... Just the small temperature differential between the surrounding air and the cooled bird's head is sufficient to generate the mechanical movement. See also Our Minto wheel Blog entry"