Even grit, which birds require in order to digest food, can become quite scarce in midwinter when the snow is deep. Many birds feed during the day only and thus require enough food to sustain warmth during the long winter nights. At 50 degrees F, there was a substantial decrease in survival time. At 5 degrees F, the House Sparrow could survive only 15 hours without food. It is critical that food is available to birds at dawn and at dusk, to enable birds to survive the long and cold Canadian nights.
Corn is a good source of carbohydrates, which in turn gives birds energy to stay warm.
Suet, is also a good source of high energy food for warmth. There are other ways to help birds endure the cold. Roosting boxes offer excellent shelter by increasing the temperature of the immediate surrounding area for the inhabitant. Another winter difficulty faced by birds is the availability of fresh water. Some birds have difficulty consuming snow as a source of water and thus fresh water is preferable.