Heated birdbaths are a great way to provide the birds a source of open water when other water sources have frozen over. Here are my Top Four Tips for Your Winter Heated Birdbath:
Keep an eye on the water level
Water evaporates faster in freezing weather because the air is dry, so make sure your heated bath doesn't go dry. Most heated birdbaths and birdbath heaters are thermostatically controlled to kick on at a certain temperature, but they do not have water sensors to shut them off when they run dry!
If you are going to be away during very cold weather, you might want to unplug your heated birdbath while you're gone so they don't run dry with the heater going.
Keep it clean
Birds can carry diseases that could pass to other birds in a birdbath. Clean your birdbath frequently, even during the winter.
Dump the debris-filled water, give it a quick wash with a stiff bristled brush, and refill with fresh water to keep your heated birdbath safe for the birds. I accomplish this by filling a 5-gallon bucket in the tub. It holds enough water to rinse, scrub, rinse, scrub again, rinse again, and refill, all in one trip.
Protect the connection between birdbath cord and extension cord
Most birdbath "failures" occur when a bit of water or moisture gets in this connection. Your goal should be to seal the connection so absolutely no moisture can enter the connection.
The easiest solution is a Lock 'n Dry Cord Set that easily seals the connection between the cord on the birdbath and a 25-foot extension cord.
The more labor intensive solution is to wrap both plugs ends completely with electrical tape. Put a small baggie around the connection, then seal the entire bag again with electrical tape.
Put a perching place in the middle
You'll notice little all-out bathing in your bath during the coldest days of winter. Birds are mostly drinking from it. Add a couple pieces of slate or some other perching spot in the middle so littler birds can more easily reach down to the water to drink.
Enjoy watching your birds take advantage of your heated birdbath all winter long!