Ooh I'll have to do this!

Yes, if you have a birdbath, or even just want to make something like this out of a bowl you have laying around, stop and check at the feed store. The heater I have just looks like a funky spiral of heater wire, wrapped in some heavy aluminum foil. While you are there, pick up a 50 lb bag of millet. Really cheap, and you just scatter it around on the ground and particularly under shrubs that give cover.

It doesn't take much to get a thing like this going in the wintertime. The water is really the thing here.

My mom always puts a heater in her bird bath in the winter. The cardinals love it!