Birds do need a source for water in the winter.

You can help birds find water by providing an open source of water for the birds. Bird baths can provide a water source and should be heated to help prevent the whole bath from freezing.
In areas where the weather can turn cold and possibly freeze the water in bird baths, a heater or heated birdbath can keep an area open in your bird bath.

  It is always a good idea to cover ceramic bird baths to keep the water out in
  the winter.
  You can put out a plastic dish with an added heater or a bird bath with a
  built-in heater.
  Some products can be kept out all winter, if the proper bird bath de-icers
  are used.