The aluminum heater for a birdbath has never been large enough for the entire birdbath, so I placed a small terracotta saucer on top of the heater. This means there's a little water in the birdbath and water in the saucer, too. I was able to catch some activity here!
Are you able to provide fresh water for the birds this Winter? In our cold climes, the water is as important as the food. Looks like this fellow enjoys the heated water! :-)