The backyard birds need water as well as food at this time of year. You can see from my photos how barren the landscape is in the Mid-Atlantic states by December. I put out a bit of food every day, and keep this stand-in birdbath refilled at least once per day.
A flexible plastic bowl from the dollar store works very well in place of my summer birdbaths. I’ve seen birds drinking and bathing in the water during this frigid weather.
Even though the water freezes solid overnight, the plastic has some give, and so far has not cracked. A concrete birdbath would likely crack and be ruined by the melt and thaw of wintertime water.
I accidentally created a birdbath by leaving a plastic bucket of gravel outdoors. This collects rainwater, giving small birds another place to drink.
Here’s an article form the Chicago Tribune with some good ideas for feeding/watering/sheltering backyard birds in the winter. Helping Birds Survive Winter in Your Backyard ~ Chicago Tribune