[david-given]

I used to have one, but I lived in a hard water area, and the felt evaporator scaled up and is stopped working.

IIRC a sipping bird is powered by the heat differential caused by cooling of the evaporator. This thing seems to be powered by centre-of-gravity changes caused by motion of hygroscopic material.

I suspect that IRL it would very quickly stop working due to gunk in the water affecting the hygroscopic material, but it's a very neat hack nevertheless.

I wonder if you could build a passive humidifier out of one of these? Float one in a container of (clean) water and attach some fan blades. As it spins, it pushes water into the air. At the very least it'd make a fun executive toy.