The frisbee I filled with water was a good start. The birds seemed to like it. But as I mentioned to my local Household Inventor, it needed improvement.
It might help if the dish was black, I said. And it might help to cover it a bit to reduce the surface area. And it might help to have some insulation underneath.
So after a bit of drilling and improvising, he produced this. He even added a windbreak. It works pretty well, too. Once I empty and refill it in the morning, the water stays liquid most of the day, even now with the weather in the 20s. The birds were all over it until the snowstorm.
So what are the birds doing?